Method: Array#permutation

Defined in:
array.c

#permutation {|element| ... } ⇒ self #permutation(n) {|element| ... } ⇒ self #permutationObject #permutation(n) ⇒ Object

When invoked with a block, yield all permutations of elements of self; returns self. The order of permutations is indeterminate.

When a block and an in-range positive Integer argument n (0 < n <= self.size) are given, calls the block with all n-tuple permutations of self.

Example:

a = [0, 1, 2]
a.permutation(2) {|permutation| p permutation }

Output:

[0, 1]
[0, 2]
[1, 0]
[1, 2]
[2, 0]
[2, 1]

Another example:

a = [0, 1, 2]
a.permutation(3) {|permutation| p permutation }

Output:

[0, 1, 2]
[0, 2, 1]
[1, 0, 2]
[1, 2, 0]
[2, 0, 1]
[2, 1, 0]

When n is zero, calls the block once with a new empty Array:

a = [0, 1, 2]
a.permutation(0) {|permutation| p permutation }

Output:

[]

When n is out of range (negative or larger than self.size), does not call the block:

a = [0, 1, 2]
a.permutation(-1) {|permutation| fail 'Cannot happen' }
a.permutation(4) {|permutation| fail 'Cannot happen' }

When a block given but no argument, behaves the same as a.permutation(a.size):

a = [0, 1, 2]
a.permutation {|permutation| p permutation }

Output:

[0, 1, 2]
[0, 2, 1]
[1, 0, 2]
[1, 2, 0]
[2, 0, 1]
[2, 1, 0]

Returns a new Enumerator if no block given:

a = [0, 1, 2]
a.permutation # => #<Enumerator: [0, 1, 2]:permutation>
a.permutation(2) # => #<Enumerator: [0, 1, 2]:permutation(2)>

Overloads:

  • #permutation {|element| ... } ⇒ self

    Yields:

    • (element)

    Returns:

    • (self)
  • #permutation(n) {|element| ... } ⇒ self

    Yields:

    • (element)

    Returns:

    • (self)

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# File 'array.c', line 6734

static VALUE
rb_ary_permutation(int argc, VALUE *argv, VALUE ary)
{
    long r, n, i;

    n = RARRAY_LEN(ary);                  /* Array length */
    RETURN_SIZED_ENUMERATOR(ary, argc, argv, rb_ary_permutation_size);   /* Return enumerator if no block */
    r = n;
    if (rb_check_arity(argc, 0, 1) && !NIL_P(argv[0]))
        r = NUM2LONG(argv[0]);            /* Permutation size from argument */

    if (r < 0 || n < r) {
	/* no permutations: yield nothing */
    }
    else if (r == 0) { /* exactly one permutation: the zero-length array */
	rb_yield(rb_ary_new2(0));
    }
    else if (r == 1) { /* this is a special, easy case */
	for (i = 0; i < RARRAY_LEN(ary); i++) {
	    rb_yield(rb_ary_new3(1, RARRAY_AREF(ary, i)));
	}
    }
    else {             /* this is the general case */
	volatile VALUE t0;
	long *p = ALLOCV_N(long, t0, r+roomof(n, sizeof(long)));
	char *used = (char*)(p + r);
	VALUE ary0 = ary_make_shared_copy(ary); /* private defensive copy of ary */
	RBASIC_CLEAR_CLASS(ary0);

	MEMZERO(used, char, n); /* initialize array */

	permute0(n, r, p, used, ary0); /* compute and yield permutations */
	ALLOCV_END(t0);
	RBASIC_SET_CLASS_RAW(ary0, rb_cArray);
    }
    return ary;
}