Class: Hash

Inherits:
Object show all
Includes:
Enumerable
Defined in:
hash.c

Overview

A Hash is a dictionary-like collection of unique keys and their values. Also called associative arrays, they are similar to Arrays, but where an Array uses integers as its index, a Hash allows you to use any object type.

Hashes enumerate their values in the order that the corresponding keys were inserted.

A Hash can be easily created by using its implicit form:

grades = { "Jane Doe" => 10, "Jim Doe" => 6 }

Hashes allow an alternate syntax for keys that are symbols. Instead of

options = { :font_size => 10, :font_family => "Arial" }

You could write it as:

options = { font_size: 10, font_family: "Arial" }

Each named key is a symbol you can access in hash:

options[:font_size]  # => 10

A Hash can also be created through its ::new method:

grades = Hash.new
grades["Dorothy Doe"] = 9

Hashes have a default value that is returned when accessing keys that do not exist in the hash. If no default is set nil is used. You can set the default value by sending it as an argument to Hash.new:

grades = Hash.new(0)

Or by using the #default= method:

grades = {"Timmy Doe" => 8}
grades.default = 0

Accessing a value in a Hash requires using its key:

puts grades["Jane Doe"] # => 0

Common Uses

Hashes are an easy way to represent data structures, such as

books         = {}
books[:matz]  = "The Ruby Programming Language"
books[:black] = "The Well-Grounded Rubyist"

Hashes are also commonly used as a way to have named parameters in functions. Note that no brackets are used below. If a hash is the last argument on a method call, no braces are needed, thus creating a really clean interface:

Person.create(name: "John Doe", age: 27)

def self.create(params)
  @name = params[:name]
  @age  = params[:age]
end

Hash Keys

Two objects refer to the same hash key when their hash value is identical and the two objects are eql? to each other.

A user-defined class may be used as a hash key if the hash and eql? methods are overridden to provide meaningful behavior. By default, separate instances refer to separate hash keys.

A typical implementation of hash is based on the object's data while eql? is usually aliased to the overridden == method:

class Book
  attr_reader :author, :title

  def initialize(author, title)
    @author = author
    @title = title
  end

  def ==(other)
    self.class === other and
      other.author == @author and
      other.title == @title
  end

  alias eql? ==

  def hash
    @author.hash ^ @title.hash # XOR
  end
end

book1 = Book.new 'matz', 'Ruby in a Nutshell'
book2 = Book.new 'matz', 'Ruby in a Nutshell'

reviews = {}

reviews[book1] = 'Great reference!'
reviews[book2] = 'Nice and compact!'

reviews.length #=> 1

See also Object#hash and Object#eql?

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Enumerable

#all?, #chain, #chunk, #chunk_while, #collect, #collect_concat, #count, #cycle, #detect, #drop, #drop_while, #each_cons, #each_entry, #each_slice, #each_with_index, #each_with_object, #entries, #filter_map, #find, #find_all, #find_index, #first, #flat_map, #grep, #grep_v, #group_by, #inject, #lazy, #map, #max, #max_by, #min, #min_by, #minmax, #minmax_by, #none?, #one?, #partition, #reduce, #reverse_each, #slice_after, #slice_before, #slice_when, #sort, #sort_by, #sum, #take, #take_while, #tally, #uniq, #zip

Constructor Details

#newObject #new(obj) ⇒ Object #new {|hash, key| ... } ⇒ Object

Returns a new, empty hash. If this hash is subsequently accessed by a key that doesn't correspond to a hash entry, the value returned depends on the style of new used to create the hash. In the first form, the access returns nil. If obj is specified, this single object will be used for all default values. If a block is specified, it will be called with the hash object and the key, and should return the default value. It is the block's responsibility to store the value in the hash if required.

h = Hash.new("Go Fish")
h["a"] = 100
h["b"] = 200
h["a"]           #=> 100
h["c"]           #=> "Go Fish"
# The following alters the single default object
h["c"].upcase!   #=> "GO FISH"
h["d"]           #=> "GO FISH"
h.keys           #=> ["a", "b"]

# While this creates a new default object each time
h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" }
h["c"]           #=> "Go Fish: c"
h["c"].upcase!   #=> "GO FISH: C"
h["d"]           #=> "Go Fish: d"
h.keys           #=> ["c", "d"]

Overloads:


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# File 'hash.c', line 1751

static VALUE
rb_hash_initialize(int argc, VALUE *argv, VALUE hash)
{
    VALUE ifnone;

    rb_hash_modify(hash);
    if (rb_block_given_p()) {
	rb_check_arity(argc, 0, 0);
	ifnone = rb_block_proc();
	SET_PROC_DEFAULT(hash, ifnone);
    }
    else {
	rb_check_arity(argc, 0, 1);
	ifnone = argc == 0 ? Qnil : argv[0];
	RHASH_SET_IFNONE(hash, ifnone);
    }

    return hash;
}

Class Method Details

.[](key, value, ...) ⇒ Object .[]([ [key, value)) ⇒ Object .[](object) ⇒ Object

Creates a new hash populated with the given objects.

Similar to the literal { key => value, ... }. In the first form, keys and values occur in pairs, so there must be an even number of arguments.

The second and third form take a single argument which is either an array of key-value pairs or an object convertible to a hash.

Hash["a", 100, "b", 200]             #=> {"a"=>100, "b"=>200}
Hash[ [ ["a", 100], ["b", 200] ] ]   #=> {"a"=>100, "b"=>200}
Hash["a" => 100, "b" => 200]         #=> {"a"=>100, "b"=>200}

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# File 'hash.c', line 1791

static VALUE
rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
{
    VALUE hash, tmp;

    if (argc == 1) {
        tmp = rb_hash_s_try_convert(Qnil, argv[0]);
	if (!NIL_P(tmp)) {
	    hash = hash_alloc(klass);
            if (RHASH_AR_TABLE_P(tmp)) {
                ar_copy(hash, tmp);
	    }
            else {
                RHASH_ST_TABLE_SET(hash, st_copy(RHASH_ST_TABLE(tmp)));
            }
	    return hash;
	}

	tmp = rb_check_array_type(argv[0]);
	if (!NIL_P(tmp)) {
	    long i;

	    hash = hash_alloc(klass);
	    for (i = 0; i < RARRAY_LEN(tmp); ++i) {
		VALUE e = RARRAY_AREF(tmp, i);
		VALUE v = rb_check_array_type(e);
		VALUE key, val = Qnil;

		if (NIL_P(v)) {
		    rb_raise(rb_eArgError, "wrong element type %s at %ld (expected array)",
			     rb_builtin_class_name(e), i);
		}
		switch (RARRAY_LEN(v)) {
		  default:
		    rb_raise(rb_eArgError, "invalid number of elements (%ld for 1..2)",
			     RARRAY_LEN(v));
		  case 2:
		    val = RARRAY_AREF(v, 1);
		  case 1:
		    key = RARRAY_AREF(v, 0);
		    rb_hash_aset(hash, key, val);
		}
	    }
	    return hash;
	}
    }
    if (argc % 2 != 0) {
	rb_raise(rb_eArgError, "odd number of arguments for Hash");
    }

    hash = hash_alloc(klass);
    rb_hash_bulk_insert(argc, argv, hash);
    hash_verify(hash);
    return hash;
}

.try_convert(obj) ⇒ Hash?

Try to convert obj into a hash, using to_hash method. Returns converted hash or nil if obj cannot be converted for any reason.

Hash.try_convert({1=>2})   # => {1=>2}
Hash.try_convert("1=>2")   # => nil

Returns:


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# File 'hash.c', line 1871

static VALUE
rb_hash_s_try_convert(VALUE dummy, VALUE hash)
{
    return rb_check_hash_type(hash);
}

Instance Method Details

#<(other) ⇒ Boolean

Returns true if hash is subset of other.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 < h2    #=> true
h2 < h1    #=> false
h1 < h1    #=> false

Returns:

  • (Boolean)

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# File 'hash.c', line 4464

static VALUE
rb_hash_lt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) >= RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}

#<=(other) ⇒ Boolean

Returns true if hash is subset of other or equals to other.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 <= h2   #=> true
h2 <= h1   #=> false
h1 <= h1   #=> true

Returns:

  • (Boolean)

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# File 'hash.c', line 4443

static VALUE
rb_hash_le(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) > RHASH_SIZE(other)) return Qfalse;
    return hash_le(hash, other);
}

#==(other_hash) ⇒ Boolean

Equality—Two hashes are equal if they each contain the same number of keys and if each key-value pair is equal to (according to Object#==) the corresponding elements in the other hash.

h1 = { "a" => 1, "c" => 2 }
h2 = { 7 => 35, "c" => 2, "a" => 1 }
h3 = { "a" => 1, "c" => 2, 7 => 35 }
h4 = { "a" => 1, "d" => 2, "f" => 35 }
h1 == h2   #=> false
h2 == h3   #=> true
h3 == h4   #=> false

The orders of each hashes are not compared.

h1 = { "a" => 1, "c" => 2 }
h2 = { "c" => 2, "a" => 1 }
h1 == h2   #=> true

Returns:

  • (Boolean)

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# File 'hash.c', line 3672

static VALUE
rb_hash_equal(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, FALSE);
}

#>(other) ⇒ Boolean

Returns true if other is subset of hash.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 > h2    #=> false
h2 > h1    #=> true
h1 > h1    #=> false

Returns:

  • (Boolean)

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# File 'hash.c', line 4506

static VALUE
rb_hash_gt(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) <= RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}

#>=(other) ⇒ Boolean

Returns true if other is subset of hash or equals to hash.

h1 = {a:1, b:2}
h2 = {a:1, b:2, c:3}
h1 >= h2   #=> false
h2 >= h1   #=> true
h1 >= h1   #=> true

Returns:

  • (Boolean)

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# File 'hash.c', line 4485

static VALUE
rb_hash_ge(VALUE hash, VALUE other)
{
    other = to_hash(other);
    if (RHASH_SIZE(hash) < RHASH_SIZE(other)) return Qfalse;
    return hash_le(other, hash);
}

#[](key) ⇒ Object

Element Reference—Retrieves the value object corresponding to the key object. If not found, returns the default value (see Hash::new for details).

h = { "a" => 100, "b" => 200 }
h["a"]   #=> 100
h["c"]   #=> nil

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# File 'hash.c', line 1993

VALUE
rb_hash_aref(VALUE hash, VALUE key)
{
    st_data_t val;

    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        return rb_hash_default_value(hash, key);
    }
}

#[]=Object

#any? {|(key, value)| ... } ⇒ Boolean #any?(pattern) ⇒ Boolean

See also Enumerable#any?

Overloads:

  • #any? {|(key, value)| ... } ⇒ Boolean

    Yields:

    • ((key, value))

    Returns:

    • (Boolean)
  • #any?(pattern) ⇒ Boolean

    Returns:

    • (Boolean)

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# File 'hash.c', line 4352

static VALUE
rb_hash_any_p(int argc, VALUE *argv, VALUE hash)
{
    VALUE args[2];
    args[0] = Qfalse;

    rb_check_arity(argc, 0, 1);
    if (RHASH_EMPTY_P(hash)) return Qfalse;
    if (argc) {
        if (rb_block_given_p()) {
            rb_warn("given block not used");
        }
	args[1] = argv[0];

	rb_hash_foreach(hash, any_p_i_pattern, (VALUE)args);
    }
    else {
	if (!rb_block_given_p()) {
	    /* yields pairs, never false */
	    return Qtrue;
	}
	if (rb_block_arity() > 1)
	    rb_hash_foreach(hash, any_p_i_fast, (VALUE)args);
	else
	    rb_hash_foreach(hash, any_p_i, (VALUE)args);
    }
    return args[0];
}

#assoc(obj) ⇒ Array?

Searches through the hash comparing obj with the key using ==. Returns the key-value pair (two elements array) or nil if no match is found. See Array#assoc.

h = {"colors"  => ["red", "blue", "green"],
     "letters" => ["a", "b", "c" ]}
h.assoc("letters")  #=> ["letters", ["a", "b", "c"]]
h.assoc("foo")      #=> nil

Returns:


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# File 'hash.c', line 4030

VALUE
rb_hash_assoc(VALUE hash, VALUE key)
{
    st_table *table;
    const struct st_hash_type *orighash;
    VALUE args[2];

    if (RHASH_EMPTY_P(hash)) return Qnil;

    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));
    table = RHASH_ST_TABLE(hash);
    orighash = table->type;

    if (orighash != &identhash) {
	VALUE value;
	struct reset_hash_type_arg ensure_arg;
	struct st_hash_type assochash;

	assochash.compare = assoc_cmp;
	assochash.hash = orighash->hash;
        table->type = &assochash;
	args[0] = hash;
	args[1] = key;
	ensure_arg.hash = hash;
	ensure_arg.orighash = orighash;
	value = rb_ensure(lookup2_call, (VALUE)&args, reset_hash_type, (VALUE)&ensure_arg);
	if (value != Qundef) return rb_assoc_new(key, value);
    }

    args[0] = key;
    args[1] = Qnil;
    rb_hash_foreach(hash, assoc_i, (VALUE)args);
    return args[1];
}

#clearHash

Removes all key-value pairs from hsh.

h = { "a" => 100, "b" => 200 }   #=> {"a"=>100, "b"=>200}
h.clear                          #=> {}

Returns:


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# File 'hash.c', line 2725

VALUE
rb_hash_clear(VALUE hash)
{
    rb_hash_modify_check(hash);

    if (RHASH_ITER_LEV(hash) > 0) {
        rb_hash_foreach(hash, clear_i, 0);
    }
    else if (RHASH_AR_TABLE_P(hash)) {
        ar_clear(hash);
    }
    else {
        st_clear(RHASH_ST_TABLE(hash));
    }

    return hash;
}

#compactObject

Returns a new hash with the nil values/key pairs removed

h = { a: 1, b: false, c: nil }
h.compact     #=> { a: 1, b: false }
h             #=> { a: 1, b: false, c: nil }

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# File 'hash.c', line 4193

static VALUE
rb_hash_compact(VALUE hash)
{
    VALUE result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
	rb_hash_foreach(hash, set_if_not_nil, result);
    }
    return result;
}

#compact!Hash?

Removes all nil values from the hash. Returns nil if no changes were made, otherwise returns the hash.

h = { a: 1, b: false, c: nil }
h.compact!     #=> { a: 1, b: false }

Returns:


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# File 'hash.c', line 4215

static VALUE
rb_hash_compact_bang(VALUE hash)
{
    st_index_t n;
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (n) {
	rb_hash_foreach(hash, delete_if_nil, hash);
        if (n != RHASH_SIZE(hash))
	    return hash;
    }
    return Qnil;
}

#compare_by_identityHash

Makes hsh compare its keys by their identity, i.e. it will consider exact same objects as same keys.

h1 = { "a" => 100, "b" => 200, :c => "c" }
h1["a"]        #=> 100
h1.compare_by_identity
h1.compare_by_identity? #=> true
h1["a".dup]    #=> nil  # different objects.
h1[:c]         #=> "c"  # same symbols are all same.

Returns:


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# File 'hash.c', line 4247

static VALUE
rb_hash_compare_by_id(VALUE hash)
{
    VALUE tmp;
    st_table *identtable;

    if (rb_hash_compare_by_id_p(hash)) return hash;

    rb_hash_modify_check(hash);
    ar_force_convert_table(hash, __FILE__, __LINE__);
    HASH_ASSERT(RHASH_ST_TABLE_P(hash));

    tmp = hash_alloc(0);
    identtable = rb_init_identtable_with_size(RHASH_SIZE(hash));
    RHASH_ST_TABLE_SET(tmp, identtable);
    rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
    st_free_table(RHASH_ST_TABLE(hash));
    RHASH_ST_TABLE_SET(hash, identtable);
    RHASH_ST_CLEAR(tmp);
    rb_gc_force_recycle(tmp);

    return hash;
}

#compare_by_identity?Boolean

Returns true if hsh will compare its keys by their identity. Also see Hash#compare_by_identity.

Returns:

  • (Boolean)

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# File 'hash.c', line 4280

MJIT_FUNC_EXPORTED VALUE
rb_hash_compare_by_id_p(VALUE hash)
{
    if (RHASH_ST_TABLE_P(hash) && RHASH_ST_TABLE(hash)->type == &identhash) {
	return Qtrue;
    }
    else {
        return Qfalse;
    }
}

#deconstruct_keys(keys) ⇒ Object


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# File 'hash.c', line 4540

static VALUE
rb_hash_deconstruct_keys(VALUE hash, VALUE keys)
{
    return hash;
}

#default(key = nil) ⇒ Object

Returns the default value, the value that would be returned by hsh if key did not exist in hsh. See also Hash::new and Hash#default=.

h = Hash.new                            #=> {}
h.default                               #=> nil
h.default(2)                            #=> nil

h = Hash.new("cat")                     #=> {}
h.default                               #=> "cat"
h.default(2)                            #=> "cat"

h = Hash.new {|h,k| h[k] = k.to_i*10}   #=> {}
h.default                               #=> nil
h.default(2)                            #=> 20

Returns:


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# File 'hash.c', line 2117

static VALUE
rb_hash_default(int argc, VALUE *argv, VALUE hash)
{
    VALUE args[2], ifnone;

    rb_check_arity(argc, 0, 1);
    ifnone = RHASH_IFNONE(hash);
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
	if (argc == 0) return Qnil;
	args[0] = hash;
	args[1] = argv[0];
	return rb_funcallv(ifnone, id_yield, 2, args);
    }
    return ifnone;
}

#default=(obj) ⇒ Object

Sets the default value, the value returned for a key that does not exist in the hash. It is not possible to set the default to a Proc that will be executed on each key lookup.

h = { "a" => 100, "b" => 200 }
h.default = "Go fish"
h["a"]     #=> 100
h["z"]     #=> "Go fish"
# This doesn't do what you might hope...
h.default = proc do |hash, key|
  hash[key] = key + key
end
h[2]       #=> #<Proc:[email protected]:6>
h["cat"]   #=> #<Proc:[email protected]:6>

Returns:


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# File 'hash.c', line 2153

static VALUE
rb_hash_set_default(VALUE hash, VALUE ifnone)
{
    rb_hash_modify_check(hash);
    SET_DEFAULT(hash, ifnone);
    return ifnone;
}

#default_procObject

If Hash::new was invoked with a block, return that block, otherwise return nil.

h = Hash.new {|h,k| h[k] = k*k }   #=> {}
p = h.default_proc                 #=> #<Proc:[email protected]:1>
a = []                             #=> []
p.call(a, 2)
a                                  #=> [nil, nil, 4]

Returns:


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# File 'hash.c', line 2176

static VALUE
rb_hash_default_proc(VALUE hash)
{
    if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
	return RHASH_IFNONE(hash);
    }
    return Qnil;
}

#default_proc=(proc_obj) ⇒ Object

Sets the default proc to be executed on each failed key lookup.

h.default_proc = proc do |hash, key|
  hash[key] = key + key
end
h[2]       #=> 4
h["cat"]   #=> "catcat"

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# File 'hash.c', line 2198

VALUE
rb_hash_set_default_proc(VALUE hash, VALUE proc)
{
    VALUE b;

    rb_hash_modify_check(hash);
    if (NIL_P(proc)) {
	SET_DEFAULT(hash, proc);
	return proc;
    }
    b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
    if (NIL_P(b) || !rb_obj_is_proc(b)) {
	rb_raise(rb_eTypeError,
		 "wrong default_proc type %s (expected Proc)",
		 rb_obj_classname(proc));
    }
    proc = b;
    SET_PROC_DEFAULT(hash, proc);
    return proc;
}

#delete(key) ⇒ Object #delete(key) {|key| ... } ⇒ Object

Deletes the key-value pair and returns the value from hsh whose key is equal to key. If the key is not found, it returns nil. If the optional code block is given and the key is not found, pass in the key and return the result of block.

h = { "a" => 100, "b" => 200 }
h.delete("a")                              #=> 100
h.delete("z")                              #=> nil
h.delete("z") { |el| "#{el} not found" }   #=> "z not found"

Overloads:

  • #delete(key) {|key| ... } ⇒ Object

    Yields:


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# File 'hash.c', line 2331

static VALUE
rb_hash_delete_m(VALUE hash, VALUE key)
{
    VALUE val;

    rb_hash_modify_check(hash);
    val = rb_hash_delete_entry(hash, key);

    if (val != Qundef) {
	return val;
    }
    else {
	if (rb_block_given_p()) {
	    return rb_yield(key);
	}
	else {
	    return Qnil;
	}
    }
}

#delete_if {|key, value| ... } ⇒ Hash #delete_ifObject

Deletes every key-value pair from hsh for which block evaluates to true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.delete_if {|key, value| key >= "b" }   #=> {"a"=>100}

Overloads:

  • #delete_if {|key, value| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 2449

VALUE
rb_hash_delete_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, delete_if_i, hash);
    }
    return hash;
}

#dig(key, ...) ⇒ Object

Extracts the nested value specified by the sequence of key objects by calling dig at each step, returning nil if any intermediate step is nil.

h = { foo: {bar: {baz: 1}}}

h.dig(:foo, :bar, :baz)     #=> 1
h.dig(:foo, :zot, :xyz)     #=> nil

g = { foo: [10, 11, 12] }
g.dig(:foo, 1)              #=> 11
g.dig(:foo, 1, 0)           #=> TypeError: Integer does not have #dig method
g.dig(:foo, :bar)           #=> TypeError: no implicit conversion of Symbol into Integer

Returns:


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# File 'hash.c', line 4400

static VALUE
rb_hash_dig(int argc, VALUE *argv, VALUE self)
{
    rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
    self = rb_hash_aref(self, *argv);
    if (!--argc) return self;
    ++argv;
    return rb_obj_dig(argc, argv, self, Qnil);
}

#each {|key, value| ... } ⇒ Hash #each_pair {|key, value| ... } ⇒ Hash #eachObject #each_pairObject

Calls block once for each key in hsh, passing the key-value pair as parameters.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each {|key, value| puts "#{key} is #{value}" }

produces:

a is 100
b is 200

Overloads:

  • #each {|key, value| ... } ⇒ Hash

    Yields:

    Returns:

  • #each_pair {|key, value| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 3029

static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (rb_block_arity() > 1)
	rb_hash_foreach(hash, each_pair_i_fast, 0);
    else
	rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}

#each_key {|key| ... } ⇒ Hash #each_keyObject

Calls block once for each key in hsh, passing the key as a parameter.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each_key {|key| puts key }

produces:

a
b

Overloads:

  • #each_key {|key| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 2982

static VALUE
rb_hash_each_key(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_key_i, 0);
    return hash;
}

#each {|key, value| ... } ⇒ Hash #each_pair {|key, value| ... } ⇒ Hash #eachObject #each_pairObject

Calls block once for each key in hsh, passing the key-value pair as parameters.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each {|key, value| puts "#{key} is #{value}" }

produces:

a is 100
b is 200

Overloads:

  • #each {|key, value| ... } ⇒ Hash

    Yields:

    Returns:

  • #each_pair {|key, value| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 3029

static VALUE
rb_hash_each_pair(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (rb_block_arity() > 1)
	rb_hash_foreach(hash, each_pair_i_fast, 0);
    else
	rb_hash_foreach(hash, each_pair_i, 0);
    return hash;
}

#each_value {|value| ... } ⇒ Hash #each_valueObject

Calls block once for each key in hsh, passing the value as a parameter.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200 }
h.each_value {|value| puts value }

produces:

100
200

Overloads:

  • #each_value {|value| ... } ⇒ Hash

    Yields:

    • (value)

    Returns:


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# File 'hash.c', line 2949

static VALUE
rb_hash_each_value(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_foreach(hash, each_value_i, 0);
    return hash;
}

#empty?Boolean

Returns true if hsh contains no key-value pairs.

{}.empty?   #=> true

Returns:

  • (Boolean)

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# File 'hash.c', line 2917

static VALUE
rb_hash_empty_p(VALUE hash)
{
    return RHASH_EMPTY_P(hash) ? Qtrue : Qfalse;
}

#eql?(other) ⇒ Boolean

Returns true if hash and other are both hashes with the same content. The orders of each hashes are not compared.

Returns:

  • (Boolean)

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# File 'hash.c', line 3687

static VALUE
rb_hash_eql(VALUE hash1, VALUE hash2)
{
    return hash_equal(hash1, hash2, TRUE);
}

#fetch(key[, default]) ⇒ Object #fetch(key) {|key| ... } ⇒ Object

Returns a value from the hash for the given key. If the key can't be found, there are several options: With no other arguments, it will raise a KeyError exception; if default is given, then that will be returned; if the optional code block is specified, then that will be run and its result returned.

h = { "a" => 100, "b" => 200 }
h.fetch("a")                            #=> 100
h.fetch("z", "go fish")                 #=> "go fish"
h.fetch("z") { |el| "go fish, #{el}"}   #=> "go fish, z"

The following example shows that an exception is raised if the key is not found and a default value is not supplied.

h = { "a" => 100, "b" => 200 }
h.fetch("z")

produces:

prog.rb:2:in `fetch': key not found (KeyError)
 from prog.rb:2

Overloads:


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# File 'hash.c', line 2054

static VALUE
rb_hash_fetch_m(int argc, VALUE *argv, VALUE hash)
{
    VALUE key;
    st_data_t val;
    long block_given;

    rb_check_arity(argc, 1, 2);
    key = argv[0];

    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
	rb_warn("block supersedes default value argument");
    }

    if (hash_stlike_lookup(hash, key, &val)) {
        return (VALUE)val;
    }
    else {
        if (block_given) {
            return rb_yield(key);
        }
        else if (argc == 1) {
            VALUE desc = rb_protect(rb_inspect, key, 0);
            if (NIL_P(desc)) {
                desc = rb_any_to_s(key);
            }
            desc = rb_str_ellipsize(desc, 65);
            rb_key_err_raise(rb_sprintf("key not found: %"PRIsVALUE, desc), hash, key);
        }
        else {
            return argv[1];
        }
    }
}

#fetch_values(key, ...) ⇒ Array #fetch_values(key, ...) {|key| ... } ⇒ Array

Returns an array containing the values associated with the given keys but also raises KeyError when one of keys can't be found. Also see Hash#values_at and Hash#fetch.

h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }

h.fetch_values("cow", "cat")                   #=> ["bovine", "feline"]
h.fetch_values("cow", "bird")                  # raises KeyError
h.fetch_values("cow", "bird") { |k| k.upcase } #=> ["bovine", "BIRD"]

Overloads:

  • #fetch_values(key, ...) ⇒ Array

    Returns:

  • #fetch_values(key, ...) {|key| ... } ⇒ Array

    Yields:

    Returns:


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# File 'hash.c', line 2596

VALUE
rb_hash_fetch_values(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;

    for (i=0; i<argc; i++) {
	rb_ary_push(result, rb_hash_fetch(hash, argv[i]));
    }
    return result;
}

#select {|key, value| ... } ⇒ Hash #selectObject #filter {|key, value| ... } ⇒ Hash #filterObject

Returns a new hash consisting of entries for which the block returns true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.select {|k,v| k > "a"}  #=> {"b" => 200, "c" => 300}
h.select {|k,v| v < 200}  #=> {"a" => 100}

Hash#filter is an alias for Hash#select.

Overloads:

  • #select {|key, value| ... } ⇒ Hash

    Yields:

    Returns:

  • #filter {|key, value| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 2635

VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
	rb_hash_foreach(hash, select_i, result);
    }
    return result;
}

#select! {|key, value| ... } ⇒ Hash? #select!Object #filter! {|key, value| ... } ⇒ Hash? #filter!Object

Equivalent to Hash#keep_if, but returns nil if no changes were made.

Hash#filter! is an alias for Hash#select!.

Overloads:

  • #select! {|key, value| ... } ⇒ Hash?

    Yields:

    Returns:

  • #filter! {|key, value| ... } ⇒ Hash?

    Yields:

    Returns:


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# File 'hash.c', line 2670

VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}

#flattenArray #flatten(level) ⇒ Array

Returns a new array that is a one-dimensional flattening of this hash. That is, for every key or value that is an array, extract its elements into the new array. Unlike Array#flatten, this method does not flatten recursively by default. The optional level argument determines the level of recursion to flatten.

a =  {1=> "one", 2 => [2,"two"], 3 => "three"}
a.flatten    # => [1, "one", 2, [2, "two"], 3, "three"]
a.flatten(2) # => [1, "one", 2, 2, "two", 3, "three"]

Overloads:


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# File 'hash.c', line 4130

static VALUE
rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
{
    VALUE ary;

    rb_check_arity(argc, 0, 1);

    if (argc) {
	int level = NUM2INT(argv[0]);

	if (level == 0) return rb_hash_to_a(hash);

	ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
	rb_hash_foreach(hash, flatten_i, ary);
	level--;

	if (level > 0) {
	    VALUE ary_flatten_level = INT2FIX(level);
	    rb_funcallv(ary, id_flatten_bang, 1, &ary_flatten_level);
	}
	else if (level < 0) {
	    /* flatten recursively */
	    rb_funcallv(ary, id_flatten_bang, 0, 0);
	}
    }
    else {
	ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
	rb_hash_foreach(hash, flatten_i, ary);
    }

    return ary;
}

#has_key?(key) ⇒ Boolean #include?(key) ⇒ Boolean #key?(key) ⇒ Boolean #member?(key) ⇒ Boolean

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that #include? and #member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

Overloads:

  • #has_key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #include?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #member?(key) ⇒ Boolean

    Returns:

    • (Boolean)

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# File 'hash.c', line 3520

MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

#has_value?(value) ⇒ Boolean #value?(value) ⇒ Boolean

Returns true if the given value is present for some key in hsh.

h = { "a" => 100, "b" => 200 }
h.value?(100)   #=> true
h.value?(999)   #=> false

Overloads:

  • #has_value?(value) ⇒ Boolean

    Returns:

    • (Boolean)
  • #value?(value) ⇒ Boolean

    Returns:

    • (Boolean)

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# File 'hash.c', line 3556

static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}

#hashInteger

Compute a hash-code for this hash. Two hashes with the same content will have the same hash code (and will compare using eql?).

See also Object#hash.

Returns:


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# File 'hash.c', line 3715

static VALUE
rb_hash_hash(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    st_index_t hval = rb_hash_start(size);
    hval = rb_hash_uint(hval, (st_index_t)rb_hash_hash);
    if (size) {
	rb_hash_foreach(hash, hash_i, (VALUE)&hval);
    }
    hval = rb_hash_end(hval);
    return ST2FIX(hval);
}

#has_key?(key) ⇒ Boolean #include?(key) ⇒ Boolean #key?(key) ⇒ Boolean #member?(key) ⇒ Boolean

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that #include? and #member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

Overloads:

  • #has_key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #include?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #member?(key) ⇒ Boolean

    Returns:

    • (Boolean)

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# File 'hash.c', line 3520

MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

#index(value) ⇒ Object

:nodoc:


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# File 'hash.c', line 2259

static VALUE
rb_hash_index(VALUE hash, VALUE value)
{
    rb_warn_deprecated("Hash#index", "Hash#key");
    return rb_hash_key(hash, value);
}

#replace(other_hash) ⇒ Hash

Replaces the contents of hsh with the contents of other_hash.

h = { "a" => 100, "b" => 200 }
h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}

Returns:


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# File 'hash.c', line 2841

static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
    }
    hash2 = to_hash(hash2);

    COPY_DEFAULT(hash, hash2);

    if (RHASH_AR_TABLE_P(hash)) {
        if (RHASH_AR_TABLE_P(hash2)) {
            ar_clear(hash);
        }
        else {
            ar_free_and_clear_table(hash);
            RHASH_ST_TABLE_SET(hash, st_init_table_with_size(RHASH_TYPE(hash2), RHASH_SIZE(hash2)));
        }
    }
    else {
        if (RHASH_AR_TABLE_P(hash2)) {
            st_free_table(RHASH_ST_TABLE(hash));
            RHASH_ST_CLEAR(hash);
        }
        else {
            st_clear(RHASH_ST_TABLE(hash));
            RHASH_TBL_RAW(hash)->type = RHASH_ST_TABLE(hash2)->type;
        }
    }
    rb_hash_foreach(hash2, rb_hash_rehash_i, (VALUE)hash);

    rb_gc_writebarrier_remember(hash);

    return hash;
}

#to_sString #inspectString Also known as: to_s

Return the contents of this hash as a string.

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
h.to_s   #=> "{\"c\"=>300, \"a\"=>100, \"d\"=>400}"

Overloads:


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# File 'hash.c', line 3324

static VALUE
rb_hash_inspect(VALUE hash)
{
    if (RHASH_EMPTY_P(hash))
	return rb_usascii_str_new2("{}");
    return rb_exec_recursive(inspect_hash, hash, 0);
}

#invertObject

Returns a new hash created by using hsh's values as keys, and the keys as values. If a key with the same value already exists in the hsh, then the last one defined will be used, the earlier value(s) will be discarded.

h = { "n" => 100, "m" => 100, "y" => 300, "d" => 200, "a" => 0 }
h.invert   #=> {0=>"a", 100=>"m", 200=>"d", 300=>"y"}

If there is no key with the same value, Hash#invert is involutive.

h = { a: 1, b: 3, c: 4 }
h.invert.invert == h #=> true

The condition, no key with the same value, can be tested by comparing the size of inverted hash.

# no key with the same value
h = { a: 1, b: 3, c: 4 }
h.size == h.invert.size #=> true

# two (or more) keys has the same value
h = { a: 1, b: 3, c: 1 }
h.size == h.invert.size #=> false

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# File 'hash.c', line 3765

static VALUE
rb_hash_invert(VALUE hash)
{
    VALUE h = rb_hash_new_with_size(RHASH_SIZE(hash));

    rb_hash_foreach(hash, rb_hash_invert_i, h);
    return h;
}

#keep_if {|key, value| ... } ⇒ Hash #keep_ifObject

Deletes every key-value pair from hsh for which block evaluates to false.

If no block is given, an enumerator is returned instead.

See also Hash#select!.

Overloads:

  • #keep_if {|key, value| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 2697

VALUE
rb_hash_keep_if(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_foreach(hash, keep_if_i, hash);
    }
    return hash;
}

#key(value) ⇒ Object

Returns the key of an occurrence of a given value. If the value is not found, returns nil.

h = { "a" => 100, "b" => 200, "c" => 300, "d" => 300 }
h.key(200)   #=> "b"
h.key(300)   #=> "c"
h.key(999)   #=> nil

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# File 'hash.c', line 2245

static VALUE
rb_hash_key(VALUE hash, VALUE value)
{
    VALUE args[2];

    args[0] = value;
    args[1] = Qnil;

    rb_hash_foreach(hash, key_i, (VALUE)args);

    return args[1];
}

#has_key?(key) ⇒ Boolean #include?(key) ⇒ Boolean #key?(key) ⇒ Boolean #member?(key) ⇒ Boolean

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that #include? and #member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

Overloads:

  • #has_key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #include?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #member?(key) ⇒ Boolean

    Returns:

    • (Boolean)

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# File 'hash.c', line 3520

MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

#keysArray

Returns a new array populated with the keys from this hash. See also Hash#values.

h = { "a" => 100, "b" => 200, "c" => 300, "d" => 400 }
h.keys   #=> ["a", "b", "c", "d"]

Returns:


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# File 'hash.c', line 3422

MJIT_FUNC_EXPORTED VALUE
rb_hash_keys(VALUE hash)
{
    st_index_t size = RHASH_SIZE(hash);
    VALUE keys =  rb_ary_new_capa(size);

    if (size == 0) return keys;

    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        RARRAY_PTR_USE_TRANSIENT(keys, ptr, {
            if (RHASH_AR_TABLE_P(hash)) {
                size = ar_keys(hash, ptr, size);
            }
            else {
                st_table *table = RHASH_ST_TABLE(hash);
                size = st_keys(table, ptr, size);
            }
        });
        rb_gc_writebarrier_remember(keys);
	rb_ary_set_len(keys, size);
    }
    else {
	rb_hash_foreach(hash, keys_i, keys);
    }

    return keys;
}

#lengthInteger #sizeInteger

Returns the number of key-value pairs in the hash.

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
h.size          #=> 4
h.delete("a")   #=> 200
h.size          #=> 3
h.length        #=> 3

Hash#length is an alias for Hash#size.

Overloads:


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# File 'hash.c', line 2895

VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}

#has_key?(key) ⇒ Boolean #include?(key) ⇒ Boolean #key?(key) ⇒ Boolean #member?(key) ⇒ Boolean

Returns true if the given key is present in hsh.

h = { "a" => 100, "b" => 200 }
h.has_key?("a")   #=> true
h.has_key?("z")   #=> false

Note that #include? and #member? do not test member equality using == as do other Enumerables.

See also Enumerable#include?

Overloads:

  • #has_key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #include?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #key?(key) ⇒ Boolean

    Returns:

    • (Boolean)
  • #member?(key) ⇒ Boolean

    Returns:

    • (Boolean)

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# File 'hash.c', line 3520

MJIT_FUNC_EXPORTED VALUE
rb_hash_has_key(VALUE hash, VALUE key)
{
    if (hash_stlike_lookup(hash, key, NULL)) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }
}

#merge(other_hash1, other_hash2, ...) ⇒ Object #merge(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object #-Object

Returns a new hash that combines the contents of the receiver and the contents of the given hashes.

If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash.

When called without any argument, returns a copy of the receiver.

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge          #=> {"a"=>100, "b"=>200}
h1.merge(h2)      #=> {"a"=>100, "b"=>246, "c"=>300}
h1.merge(h2, h3)  #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1.merge(h2) {|key, oldval, newval| newval - oldval}
                  #=> {"a"=>100, "b"=>46,  "c"=>300}
h1.merge(h2, h3) {|key, oldval, newval| newval - oldval}
                  #=> {"a"=>100, "b"=>311, "c"=>300, "d"=>400}
h1                #=> {"a"=>100, "b"=>200}

Overloads:

  • #merge(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object

    Yields:

    • (key, oldval, newval)

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# File 'hash.c', line 3971

static VALUE
rb_hash_merge(int argc, VALUE *argv, VALUE self)
{
    return rb_hash_update(argc, argv, rb_hash_dup(self));
}

#merge!(other_hash1, other_hash2, ...) ⇒ Hash #update(other_hash1, other_hash2, ...) ⇒ Hash #merge!(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object #-Object #update(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object #-Object

Adds the contents of the given hashes to the receiver.

If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash.

h1 = { "a" => 100, "b" => 200 }
h1.merge!          #=> {"a"=>100, "b"=>200}
h1                 #=> {"a"=>100, "b"=>200}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h1.merge!(h2)      #=> {"a"=>100, "b"=>246, "c"=>300}
h1                 #=> {"a"=>100, "b"=>246, "c"=>300}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3)
                   #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3) {|key, v1, v2| v1 }
                   #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}

Hash#update is an alias for Hash#merge!.

Overloads:

  • #merge!(other_hash1, other_hash2, ...) ⇒ Hash

    Returns:

  • #update(other_hash1, other_hash2, ...) ⇒ Hash

    Returns:

  • #merge!(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object

    Yields:

    • (key, oldval, newval)
  • #update(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object

    Yields:

    • (key, oldval, newval)

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# File 'hash.c', line 3867

static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
    int i;
    bool block_given = rb_block_given_p();

    rb_hash_modify(self);
    for (i = 0; i < argc; i++){
       VALUE hash = to_hash(argv[i]);
       if (block_given) {
           rb_hash_foreach(hash, rb_hash_update_block_i, self);
       }
       else {
           rb_hash_foreach(hash, rb_hash_update_i, self);
       }
    }
    return self;
}

#rassoc(obj) ⇒ Array?

Searches through the hash comparing obj with the value using ==. Returns the first key-value pair (two-element array) that matches. See also Array#rassoc.

a = {1=> "one", 2 => "two", 3 => "three", "ii" => "two"}
a.rassoc("two")    #=> [2, "two"]
a.rassoc("four")   #=> nil

Returns:


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# File 'hash.c', line 4091

VALUE
rb_hash_rassoc(VALUE hash, VALUE obj)
{
    VALUE args[2];

    args[0] = obj;
    args[1] = Qnil;
    rb_hash_foreach(hash, rassoc_i, (VALUE)args);
    return args[1];
}

#rehashHash

Rebuilds the hash based on the current hash values for each key. If values of key objects have changed since they were inserted, this method will reindex hsh. If Hash#rehash is called while an iterator is traversing the hash, a RuntimeError will be raised in the iterator.

a = [ "a", "b" ]
c = [ "c", "d" ]
h = { a => 100, c => 300 }
h[a]       #=> 100
a[0] = "z"
h[a]       #=> nil
h.rehash   #=> {["z", "b"]=>100, ["c", "d"]=>300}
h[a]       #=> 100

Returns:


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# File 'hash.c', line 1914

VALUE
rb_hash_rehash(VALUE hash)
{
    VALUE tmp;
    st_table *tbl;

    if (RHASH_ITER_LEV(hash) > 0) {
	rb_raise(rb_eRuntimeError, "rehash during iteration");
    }
    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
        tmp = hash_alloc(0);
        ar_alloc_table(tmp);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        ar_free_and_clear_table(hash);
        ar_copy(hash, tmp);
        ar_free_and_clear_table(tmp);
    }
    else if (RHASH_ST_TABLE_P(hash)) {
        st_table *old_tab = RHASH_ST_TABLE(hash);
        tmp = hash_alloc(0);
        tbl = st_init_table_with_size(old_tab->type, old_tab->num_entries);
        RHASH_ST_TABLE_SET(tmp, tbl);
        rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
        st_free_table(old_tab);
        RHASH_ST_TABLE_SET(hash, tbl);
        RHASH_ST_CLEAR(tmp);
    }
    hash_verify(hash);
    return hash;
}

#reject {|key, value| ... } ⇒ Hash #rejectObject

Returns a new hash consisting of entries for which the block returns false.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.reject {|k,v| k < "b"}  #=> {"b" => 200, "c" => 300}
h.reject {|k,v| v > 100}  #=> {"a" => 100}

Overloads:

  • #reject {|key, value| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 2506

VALUE
rb_hash_reject(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    if (RTEST(ruby_verbose)) {
	VALUE klass;
	if (HAS_EXTRA_STATES(hash, klass)) {
	    rb_warn("extra states are no longer copied: %+"PRIsVALUE, hash);
	}
    }
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
	rb_hash_foreach(hash, reject_i, result);
    }
    return result;
}

#reject! {|key, value| ... } ⇒ Hash? #reject!Object

Equivalent to Hash#delete_if, but returns nil if no changes were made.

Overloads:

  • #reject! {|key, value| ... } ⇒ Hash?

    Yields:

    Returns:


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# File 'hash.c', line 2469

VALUE
rb_hash_reject_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, delete_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}

#replace(other_hash) ⇒ Hash

Replaces the contents of hsh with the contents of other_hash.

h = { "a" => 100, "b" => 200 }
h.replace({ "c" => 300, "d" => 400 })   #=> {"c"=>300, "d"=>400}

Returns:


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# File 'hash.c', line 2841

static VALUE
rb_hash_replace(VALUE hash, VALUE hash2)
{
    rb_hash_modify_check(hash);
    if (hash == hash2) return hash;
    if (RHASH_ITER_LEV(hash) > 0) {
        rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
    }
    hash2 = to_hash(hash2);

    COPY_DEFAULT(hash, hash2);

    if (RHASH_AR_TABLE_P(hash)) {
        if (RHASH_AR_TABLE_P(hash2)) {
            ar_clear(hash);
        }
        else {
            ar_free_and_clear_table(hash);
            RHASH_ST_TABLE_SET(hash, st_init_table_with_size(RHASH_TYPE(hash2), RHASH_SIZE(hash2)));
        }
    }
    else {
        if (RHASH_AR_TABLE_P(hash2)) {
            st_free_table(RHASH_ST_TABLE(hash));
            RHASH_ST_CLEAR(hash);
        }
        else {
            st_clear(RHASH_ST_TABLE(hash));
            RHASH_TBL_RAW(hash)->type = RHASH_ST_TABLE(hash2)->type;
        }
    }
    rb_hash_foreach(hash2, rb_hash_rehash_i, (VALUE)hash);

    rb_gc_writebarrier_remember(hash);

    return hash;
}

#select {|key, value| ... } ⇒ Hash #selectObject #filter {|key, value| ... } ⇒ Hash #filterObject

Returns a new hash consisting of entries for which the block returns true.

If no block is given, an enumerator is returned instead.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.select {|k,v| k > "a"}  #=> {"b" => 200, "c" => 300}
h.select {|k,v| v < 200}  #=> {"a" => 100}

Hash#filter is an alias for Hash#select.

Overloads:

  • #select {|key, value| ... } ⇒ Hash

    Yields:

    Returns:

  • #filter {|key, value| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 2635

VALUE
rb_hash_select(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
	rb_hash_foreach(hash, select_i, result);
    }
    return result;
}

#select! {|key, value| ... } ⇒ Hash? #select!Object #filter! {|key, value| ... } ⇒ Hash? #filter!Object

Equivalent to Hash#keep_if, but returns nil if no changes were made.

Hash#filter! is an alias for Hash#select!.

Overloads:

  • #select! {|key, value| ... } ⇒ Hash?

    Yields:

    Returns:

  • #filter! {|key, value| ... } ⇒ Hash?

    Yields:

    Returns:


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# File 'hash.c', line 2670

VALUE
rb_hash_select_bang(VALUE hash)
{
    st_index_t n;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);
    n = RHASH_SIZE(hash);
    if (!n) return Qnil;
    rb_hash_foreach(hash, keep_if_i, hash);
    if (n == RHASH_SIZE(hash)) return Qnil;
    return hash;
}

#shiftArray, Object

Removes a key-value pair from hsh and returns it as the two-item array [ key, value ], or the hash's default value if the hash is empty.

h = { 1 => "a", 2 => "b", 3 => "c" }
h.shift   #=> [1, "a"]
h         #=> {2=>"b", 3=>"c"}

Returns:


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# File 'hash.c', line 2380

static VALUE
rb_hash_shift(VALUE hash)
{
    struct shift_var var;

    rb_hash_modify_check(hash);
    if (RHASH_AR_TABLE_P(hash)) {
	var.key = Qundef;
	if (RHASH_ITER_LEV(hash) == 0) {
            if (ar_shift(hash, &var.key, &var.val)) {
		return rb_assoc_new(var.key, var.val);
	    }
	}
	else {
            rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
            if (var.key != Qundef) {
                rb_hash_delete_entry(hash, var.key);
                return rb_assoc_new(var.key, var.val);
            }
        }
    }
    if (RHASH_ST_TABLE_P(hash)) {
        var.key = Qundef;
        if (RHASH_ITER_LEV(hash) == 0) {
            if (st_shift(RHASH_ST_TABLE(hash), &var.key, &var.val)) {
                return rb_assoc_new(var.key, var.val);
            }
        }
        else {
	    rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
	    if (var.key != Qundef) {
		rb_hash_delete_entry(hash, var.key);
		return rb_assoc_new(var.key, var.val);
	    }
	}
    }
    return rb_hash_default_value(hash, Qnil);
}

#lengthInteger #sizeInteger

Returns the number of key-value pairs in the hash.

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 }
h.size          #=> 4
h.delete("a")   #=> 200
h.size          #=> 3
h.length        #=> 3

Hash#length is an alias for Hash#size.

Overloads:


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# File 'hash.c', line 2895

VALUE
rb_hash_size(VALUE hash)
{
    return INT2FIX(RHASH_SIZE(hash));
}

#slice(*keys) ⇒ Hash

Returns a hash containing only the given keys and their values.

h = { a: 100, b: 200, c: 300 }
h.slice(:a)           #=> {:a=>100}
h.slice(:b, :c, :d)   #=> {:b=>200, :c=>300}

Returns:


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# File 'hash.c', line 2536

static VALUE
rb_hash_slice(int argc, VALUE *argv, VALUE hash)
{
    int i;
    VALUE key, value, result;

    if (argc == 0 || RHASH_EMPTY_P(hash)) {
	return rb_hash_new();
    }
    result = rb_hash_new_with_size(argc);

    for (i = 0; i < argc; i++) {
	key = argv[i];
	value = rb_hash_lookup2(hash, key, Qundef);
	if (value != Qundef)
	    rb_hash_aset(result, key, value);
    }

    return result;
}

#storeObject

#to_aArray

Converts hsh to a nested array of [ key, value ] arrays.

h = { "c" => 300, "a" => 100, "d" => 400, "c" => 300  }
h.to_a   #=> [["c", 300], ["a", 100], ["d", 400]]

Returns:


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# File 'hash.c', line 3269

static VALUE
rb_hash_to_a(VALUE hash)
{
    VALUE ary;

    ary = rb_ary_new_capa(RHASH_SIZE(hash));
    rb_hash_foreach(hash, to_a_i, ary);

    return ary;
}

#to_hHash #to_h {|key, value| ... } ⇒ Object

Returns self. If called on a subclass of Hash, converts the receiver to a Hash object.

If a block is given, the results of the block on each pair of the receiver will be used as pairs.

Overloads:

  • #to_hHash

    Returns:

  • #to_h {|key, value| ... } ⇒ Object

    Yields:


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# File 'hash.c', line 3390

static VALUE
rb_hash_to_h(VALUE hash)
{
    if (rb_block_given_p()) {
        return rb_hash_to_h_block(hash);
    }
    if (rb_obj_class(hash) != rb_cHash) {
	const VALUE flags = RBASIC(hash)->flags;
        hash = hash_dup(hash, rb_cHash, flags & RHASH_PROC_DEFAULT);
    }
    return hash;
}

#to_hashHash

Returns self.

Returns:


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# File 'hash.c', line 3339

static VALUE
rb_hash_to_hash(VALUE hash)
{
    return hash;
}

#to_procProc

Returns a Proc which maps keys to values.

h = {a:1, b:2}
hp = h.to_proc
hp.call(:a)          #=> 1
hp.call(:b)          #=> 2
hp.call(:c)          #=> nil
[:a, :b, :c].map(&h) #=> [1, 2, nil]

Returns:


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# File 'hash.c', line 4534

static VALUE
rb_hash_to_proc(VALUE hash)
{
    return rb_func_proc_new(hash_proc_call, hash);
}

#transform_keys {|key| ... } ⇒ Object #transform_keysObject

Returns a new hash with the results of running the block once for every key. This method does not change the values.

h = { a: 1, b: 2, c: 3 }
h.transform_keys {|k| k.to_s }  #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys(&:to_s)        #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys.with_index {|k, i| "#{k}.#{i}" }
                                #=> { "a.0" => 1, "b.1" => 2, "c.2" => 3 }

If no block is given, an enumerator is returned instead.

Overloads:

  • #transform_keys {|key| ... } ⇒ Object

    Yields:


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# File 'hash.c', line 3087

static VALUE
rb_hash_transform_keys(int argc, VALUE *argv, VALUE hash)
{
    VALUE result;
    struct transform_keys_args transarg = {0};

    argc = rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        transarg.trans = to_hash(argv[0]);
        transarg.block_given = rb_block_given_p();
    }
    else {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    }
    result = rb_hash_new();
    if (!RHASH_EMPTY_P(hash)) {
        if (transarg.trans) {
            transarg.result = result;
            rb_hash_foreach(hash, transform_keys_hash_i, (VALUE)&transarg);
        }
        else {
            rb_hash_foreach(hash, transform_keys_i, result);
        }
    }

    return result;
}

#transform_keys! {|key| ... } ⇒ Hash #transform_keys!Object

Invokes the given block once for each key in hsh, replacing it with the new key returned by the block, and then returns hsh. This method does not change the values.

h = { a: 1, b: 2, c: 3 }
h.transform_keys! {|k| k.to_s }  #=> { "a" => 1, "b" => 2, "c" => 3 }
h.transform_keys!(&:to_sym)      #=> { a: 1, b: 2, c: 3 }
h.transform_keys!.with_index {|k, i| "#{k}.#{i}" }
                                 #=> { "a.0" => 1, "b.1" => 2, "c.2" => 3 }

If no block is given, an enumerator is returned instead.

Overloads:

  • #transform_keys! {|key| ... } ⇒ Hash

    Yields:

    Returns:


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# File 'hash.c', line 3134

static VALUE
rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
{
    VALUE trans = 0;
    int block_given = 0;

    argc = rb_check_arity(argc, 0, 1);
    if (argc > 0) {
        trans = to_hash(argv[0]);
        block_given = rb_block_given_p();
    }
    else {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    }
    rb_hash_modify_check(hash);
    if (!RHASH_TABLE_EMPTY_P(hash)) {
        long i;
        VALUE pairs = rb_hash_flatten(0, NULL, hash);
        rb_hash_clear(hash);
        for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
            VALUE key = RARRAY_AREF(pairs, i), new_key, val;

            if (!trans) {
                new_key = rb_yield(key);
            }
            else if ((new_key = rb_hash_lookup2(trans, key, Qundef)) != Qundef) {
                /* use the transformed key */
            }
            else if (block_given) {
                new_key = rb_yield(key);
            }
            else {
                new_key = key;
            }
            val = RARRAY_AREF(pairs, i+1);
            rb_hash_aset(hash, new_key, val);
        }
    }
    return hash;
}

#transform_values {|value| ... } ⇒ Object #transform_valuesObject

Returns a new hash with the results of running the block once for every value. This method does not change the keys.

h = { a: 1, b: 2, c: 3 }
h.transform_values {|v| v * v + 1 }  #=> { a: 2, b: 5, c: 10 }
h.transform_values(&:to_s)           #=> { a: "1", b: "2", c: "3" }
h.transform_values.with_index {|v, i| "#{v}.#{i}" }
                                     #=> { a: "1.0", b: "2.1", c: "3.2" }

If no block is given, an enumerator is returned instead.

Overloads:

  • #transform_values {|value| ... } ⇒ Object

    Yields:

    • (value)

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# File 'hash.c', line 3206

static VALUE
rb_hash_transform_values(VALUE hash)
{
    VALUE result;

    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    result = hash_dup(hash, rb_cHash, 0);

    if (!RHASH_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(result, transform_values_foreach_func, transform_values_foreach_replace, 0);
    }

    return result;
}

#transform_values! {|value| ... } ⇒ Hash #transform_values!Object

Invokes the given block once for each value in hsh, replacing it with the new value returned by the block, and then returns hsh. This method does not change the keys.

h = { a: 1, b: 2, c: 3 }
h.transform_values! {|v| v * v + 1 }  #=> { a: 2, b: 5, c: 10 }
h.transform_values!(&:to_s)           #=> { a: "2", b: "5", c: "10" }
h.transform_values!.with_index {|v, i| "#{v}.#{i}" }
                                      #=> { a: "2.0", b: "5.1", c: "10.2" }

If no block is given, an enumerator is returned instead.

Overloads:

  • #transform_values! {|value| ... } ⇒ Hash

    Yields:

    • (value)

    Returns:


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# File 'hash.c', line 3238

static VALUE
rb_hash_transform_values_bang(VALUE hash)
{
    RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
    rb_hash_modify_check(hash);

    if (!RHASH_TABLE_EMPTY_P(hash)) {
        rb_hash_stlike_foreach_with_replace(hash, transform_values_foreach_func, transform_values_foreach_replace, 0);
    }

    return hash;
}

#merge!(other_hash1, other_hash2, ...) ⇒ Hash #update(other_hash1, other_hash2, ...) ⇒ Hash #merge!(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object #-Object #update(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object #-Object

Adds the contents of the given hashes to the receiver.

If no block is given, entries with duplicate keys are overwritten with the values from each other_hash successively, otherwise the value for each duplicate key is determined by calling the block with the key, its value in the receiver and its value in each other_hash.

h1 = { "a" => 100, "b" => 200 }
h1.merge!          #=> {"a"=>100, "b"=>200}
h1                 #=> {"a"=>100, "b"=>200}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h1.merge!(h2)      #=> {"a"=>100, "b"=>246, "c"=>300}
h1                 #=> {"a"=>100, "b"=>246, "c"=>300}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3)
                   #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>357, "c"=>300, "d"=>400}

h1 = { "a" => 100, "b" => 200 }
h2 = { "b" => 246, "c" => 300 }
h3 = { "b" => 357, "d" => 400 }
h1.merge!(h2, h3) {|key, v1, v2| v1 }
                   #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}
h1                 #=> {"a"=>100, "b"=>200, "c"=>300, "d"=>400}

Hash#update is an alias for Hash#merge!.

Overloads:

  • #merge!(other_hash1, other_hash2, ...) ⇒ Hash

    Returns:

  • #update(other_hash1, other_hash2, ...) ⇒ Hash

    Returns:

  • #merge!(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object

    Yields:

    • (key, oldval, newval)
  • #update(other_hash1, other_hash2, ...) {|key, oldval, newval| ... } ⇒ Object

    Yields:

    • (key, oldval, newval)

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# File 'hash.c', line 3867

static VALUE
rb_hash_update(int argc, VALUE *argv, VALUE self)
{
    int i;
    bool block_given = rb_block_given_p();

    rb_hash_modify(self);
    for (i = 0; i < argc; i++){
       VALUE hash = to_hash(argv[i]);
       if (block_given) {
           rb_hash_foreach(hash, rb_hash_update_block_i, self);
       }
       else {
           rb_hash_foreach(hash, rb_hash_update_i, self);
       }
    }
    return self;
}

#has_value?(value) ⇒ Boolean #value?(value) ⇒ Boolean

Returns true if the given value is present for some key in hsh.

h = { "a" => 100, "b" => 200 }
h.value?(100)   #=> true
h.value?(999)   #=> false

Overloads:

  • #has_value?(value) ⇒ Boolean

    Returns:

    • (Boolean)
  • #value?(value) ⇒ Boolean

    Returns:

    • (Boolean)

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# File 'hash.c', line 3556

static VALUE
rb_hash_has_value(VALUE hash, VALUE val)
{
    VALUE data[2];

    data[0] = Qfalse;
    data[1] = val;
    rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
    return data[0];
}

#valuesArray

Returns a new array populated with the values from hsh. See also Hash#keys.

h = { "a" => 100, "b" => 200, "c" => 300 }
h.values   #=> [100, 200, 300]

Returns:


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# File 'hash.c', line 3469

VALUE
rb_hash_values(VALUE hash)
{
    VALUE values;
    st_index_t size = RHASH_SIZE(hash);

    values = rb_ary_new_capa(size);
    if (size == 0) return values;

    if (ST_DATA_COMPATIBLE_P(VALUE)) {
        if (RHASH_AR_TABLE_P(hash)) {
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = ar_values(hash, ptr, size);
            });
        }
        else if (RHASH_ST_TABLE_P(hash)) {
            st_table *table = RHASH_ST_TABLE(hash);
            rb_gc_writebarrier_remember(values);
            RARRAY_PTR_USE_TRANSIENT(values, ptr, {
                size = st_values(table, ptr, size);
            });
        }
	rb_ary_set_len(values, size);
    }
    else {
	rb_hash_foreach(hash, values_i, values);
    }

    return values;
}

#values_at(key, ...) ⇒ Array

Return an array containing the values associated with the given keys. Also see Hash.select.

h = { "cat" => "feline", "dog" => "canine", "cow" => "bovine" }
h.values_at("cow", "cat")  #=> ["bovine", "feline"]

Returns:


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# File 'hash.c', line 2568

VALUE
rb_hash_values_at(int argc, VALUE *argv, VALUE hash)
{
    VALUE result = rb_ary_new2(argc);
    long i;

    for (i=0; i<argc; i++) {
	rb_ary_push(result, rb_hash_aref(hash, argv[i]));
    }
    return result;
}