Class: Table
Overview
This class is a Ruby representation of a table. All data is captured as type String
by default. Columns are referred to by their String
headers which are assumed to be identified in the first row of the input file. Output is written by default to tab-delimited files with the first row serving as the header names.
Instance Attribute Summary collapse
-
#headers ⇒ Object
readonly
The headers attribute contains the table headers used to reference columns in the
Table
.
Instance Method Summary collapse
-
#add_column(*args) ⇒ Object
Add a column to the Table.
-
#add_row(*row) ⇒ Object
(also: #<<)
Add a row to the Table, appending it to the end.
-
#add_rows(array_of_rows) ⇒ Object
Add one or more rows to the Table, appending it to the end.
-
#bottom(colname, num = 1) ⇒ Object
Returns counts of the least frequent values found in a given column in the form of a Table.
-
#column(colname) ⇒ Object
Return a copy of a column from the table, identified by column name.
-
#count(colname = nil, value = nil) ⇒ Object
(also: #size, #length)
Counts the number of instances of a particular string, given a column name, and returns an integer >= 0.
-
#del_column(colname) ⇒ Object
Delete a column from the Table.
-
#del_row(rownum) ⇒ Object
Delete a row from the Table.
-
#each ⇒ Object
Defines an iterator for
Table
which produces rows of data (headers omitted) for its calling block. -
#empty? ⇒ Boolean
Return true if the Table is empty, false otherwise.
-
#initialize(input = nil) ⇒ Table
constructor
Instantiate a
Table
object using a tab-delimited file. -
#intersect(table2, colname, col2name = colname) ⇒ Object
Return an Array with the intersection of columns from different tables, eliminating duplicates.
-
#join(table2, colname, col2name = colname) ⇒ Object
Given a second table to join against, and a field/column, return a
Table
which contains a join of the two tables. -
#row(index) ⇒ Object
Return a copy of a row from the table as an
Array
, given an index (i.e. row number). -
#select(*columns) ⇒ Object
(also: #get_columns)
Select columns from the table, given one or more column names.
-
#sort(column = nil, &block) ⇒ Object
(also: #sort!)
Sort the table based on given column.
-
#sub(colname, re = nil, replace = nil, &block) ⇒ Object
Given a field/column, and a regular expression to match against, and a replacement string, create a new table which performs a substitute operation on column data.
-
#tally(colname) ⇒ Object
Count instances in a particular field/column and return a
Table
of the results. -
#to_a ⇒ Object
Converts a
Table
object to an array of arrays (each row). -
#to_s ⇒ Object
Converts a
Table
object to a tab-delimited string. -
#top(colname, num = 1) ⇒ Object
Returns counts of the most frequent values found in a given column in the form of a Table.
-
#union(table2, colname, col2name = colname) ⇒ Object
Return Array with the union of elements columns in the given tables, eliminating duplicates.
-
#where(colname, condition = nil) ⇒ Object
(also: #get_rows)
Given a particular condition for a given column field/column, return a subtable that matches the condition.
-
#write_file(filename) ⇒ Object
Write a representation of the
Table
object to a file (tab delimited).
Constructor Details
#initialize(input = nil) ⇒ Table
Instantiate a Table
object using a tab-delimited file
Attributes
input
-
OPTIONAL
Array
of rows orString
to identify the name of the tab-delimited file to read
Examples
cities = Table.new() # empty table
cities = Table.new([ ["City", "State], ["New York", "NY"], ["Dallas", "TX"] ]) # create from Array of rows
cities = Table.new("cities.txt") # read from file
cities = Table.new(capitals) # create from table
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# File 'lib/tablestakes.rb', line 43 def initialize(input=nil) @headers = [] @table = {} @indices = {} if input.respond_to?(:fetch) if input[0].respond_to?(:fetch) #create Table from rows add_rows(input) end elsif input.respond_to?(:upcase) # a string, then read_file read_file(input) elsif input.respond_to?(:headers) input.each {|row| add_row(row) } end # else create empty +Table+ end |
Instance Attribute Details
#headers ⇒ Object (readonly)
The headers attribute contains the table headers used to reference columns in the Table
. All headers are represented as String
types.
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# File 'lib/tablestakes.rb', line 24 def headers @headers end |
Instance Method Details
#add_column(*args) ⇒ Object
Add a column to the Table. Raises ArgumentError if the column name is already taken or there are not the correct number of values.
Attributes
args
-
Array of
String
to identify the name of the column (see examples)
Examples
cities.add_column("City", ["New York", "Dallas", "San Franscisco"])
cities.add_column(["City","New York", "Dallas", "San Franscisco"])
cities.add_column("City", "New York", "Dallas", "San Franscisco")
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# File 'lib/tablestakes.rb', line 114 def add_column(*args) if args.kind_of? Array args.flatten! colname = args.shift column_vals = args else raise ArgumentError, "Invalid Arguments to add_column" end # check arguments raise ArgumentError, "Duplicate Column Name!" if @table.has_key?(colname) unless self.empty? if column_vals.length != @table[@headers.first].length raise ArgumentError, "Number of elements in column does not match existing table" end end append_col(colname, column_vals) end |
#add_row(*row) ⇒ Object Also known as: <<
Add a row to the Table, appending it to the end. Raises ArgumentError if there are not the correct number of values.
Attributes
row
-
Array
to hold the row values
Examples
cities = Table.new.add_row( ["City", "State"] ) # create new Table with headers
cities.add_row("New York", "NY") # add data row to Table
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# File 'lib/tablestakes.rb', line 158 def add_row(*row) if row.kind_of? Array row = row.flatten else raise ArgumentError, "Invalid Arguments to add_row" end if @headers.empty? @headers = row else unless row.length == @headers.length raise ArgumentError, "Wrong number of fields in Table input" end append_row(row) end return self end |
#add_rows(array_of_rows) ⇒ Object
Add one or more rows to the Table, appending it to the end. Raises ArgumentError if there are not the correct number of values. The first row becomes the table headers if currently undefined.
Attributes
array_of_rows
-
Array
ofArrays
to hold the rows values
Examples
cities.add_rows([ ["New York", "NY"], ["Austin", "TX"] ])
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# File 'lib/tablestakes.rb', line 141 def add_rows(array_of_rows) array_of_rows.each do |r| add_row(r.clone) end return self end |
#bottom(colname, num = 1) ⇒ Object
Returns counts of the least frequent values found in a given column in the form of a Table. Raises ArgumentError if the column is not found. If no limit is given to the number of values, only the least frequent value will be returned.
Attributes
colname
-
String
to identify the column to count num
-
OPTIONAL
String
number of values to return
Examples
cities.bottom("State") # returns a Table with the least frequent state in the cities Table
cities.bottom("State", 10) # returns a Table with the 10 least frequent states in the cities Table
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# File 'lib/tablestakes.rb', line 320 def bottom(colname, num=1) freq = tally(colname).to_a[1..-1].sort_by {|k,v| v } return Table.new(freq[0..num-1].unshift([colname,"Count"])) end |
#column(colname) ⇒ Object
Return a copy of a column from the table, identified by column name. Returns empty Array if column name not found.
Attributes
colname
-
String
to identify the name of the column
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# File 'lib/tablestakes.rb', line 80 def column(colname) # return empty Array if column name not found unless @table.has_key?(colname) Array.new() else Array(@table[colname]) end end |
#count(colname = nil, value = nil) ⇒ Object Also known as: size, length
Counts the number of instances of a particular string, given a column name, and returns an integer >= 0. Returns nil
if the column is not found. If no parameters are given, returns the number of rows in the table.
Attributes
colname
-
OPTIONAL
String
to identify the column to count value
-
OPTIONAL
String
value to count
Examples
cities.count # returns number of rows in cities Table
cities.size # same as cities.count
cities.length # same as cities.count
cities.count("State", "NY") # returns the number of rows with State == "NY"
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# File 'lib/tablestakes.rb', line 266 def count(colname=nil, value=nil) if colname.nil? || value.nil? if @table.size > 0 @table.each_key {|e| return @table.fetch(e).length } else return 0 end end raise ArgumentError, "Invalid column name" unless @headers.include?(colname) if @table[colname] result = 0 @table[colname].each do |val| val == value.to_s ? result += 1 : nil end result else nil end end |
#del_column(colname) ⇒ Object
Delete a column from the Table. Raises ArgumentError if the column name does not exist.
Attributes
colname
-
String
to identify the name of the column
Examples
cities.del_column("State") # returns table without "State" column
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# File 'lib/tablestakes.rb', line 184 def del_column(colname) # check arguments raise ArgumentError, "Column name does not exist!" unless @table.has_key?(colname) @headers.delete(colname) @table.delete(colname) return self end |
#del_row(rownum) ⇒ Object
Delete a row from the Table. Raises ArgumentError if the row number is not found
Attributes
rownum
-
FixNum
to hold the row number
Examples
cities.del_row(3) # deletes row with index 3 (4th row)
cities.del_row(-1) # deletes last row (per Ruby convention)
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# File 'lib/tablestakes.rb', line 202 def del_row(rownum) # check arguments if self.empty? || rownum >= @table[@headers.first].length raise ArgumentError, "Row number does not exist!" end @headers.each do |col| @table[col].delete_at(rownum) end return self end |
#each ⇒ Object
Defines an iterator for Table
which produces rows of data (headers omitted) for its calling block.
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# File 'lib/tablestakes.rb', line 65 def each @table[@headers.first].each_index do |index| nextrow = [] @headers.each do |col| nextrow << @table[col][index].clone end yield nextrow end end |
#empty? ⇒ Boolean
Return true if the Table is empty, false otherwise.
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# File 'lib/tablestakes.rb', line 100 def empty? @headers.length == 0 && @table.length == 0 end |
#intersect(table2, colname, col2name = colname) ⇒ Object
Return an Array with the intersection of columns from different tables, eliminating duplicates. Return nil if a column is not found.
Attributes
table2
-
Table
to identify the secondary table in the intersection colname
-
String
to identify the column to intersection col2name
-
OPTIONAL
String
to identify the column in the second table to intersection
Examples
cities.intersect(capitals, "City", "Capital") # returns Array with all capitals that are also in the cities table
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# File 'lib/tablestakes.rb', line 530 def intersect(table2, colname, col2name=colname) # check arguments raise ArgumentError, "Invalid table!" unless table2.is_a?(Table) raise ArgumentError, "Invalid column name" unless @table.has_key?(colname) raise ArgumentError, "Invalid column name" unless table2.headers.include?(col2name) return self.column(colname) & table2.column(col2name) end |
#join(table2, colname, col2name = colname) ⇒ Object
Given a second table to join against, and a field/column, return a Table
which contains a join of the two tables. Join only lists the common column once, under the column name of the first table (if different from the name of thee second). All columns from both tables are returned. Returns nil
if the column is not found.
Attributes
table2
-
Table
to identify the secondary table in the join colname
-
String
to identify the column to join on col2name
-
OPTIONAL
String
to identify the column in the second table to join on
Examples
cities.join(capitals, "City", "Capital") # returns a Table of cities that are also state capitals
capitals.join(cities, "State") # returns a Table of capital cities with populations info from the cities table
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# File 'lib/tablestakes.rb', line 427 def join(table2, colname, col2name=colname) # check arguments raise ArgumentError, "Invalid table!" unless table2.is_a?(Table) raise ArgumentError, "Invalid column name" unless @table.has_key?(colname) raise ArgumentError, "Invalid column name" unless table2.headers.include?(col2name) t2_col_index = table2.headers.index(col2name) dedupe_headers(table2, colname) result = [ Array(@headers) + Array(table2.headers) ] @table[colname].each_index do |index| t2_index = table2.column(col2name).find_index(@table[colname][index]) unless t2_index.nil? result << self.row(index) + table2.row(t2_index) end end if result.length == 1 #no rows selected return nil else return Table.new(result) end end |
#row(index) ⇒ Object
Return a copy of a row from the table as an Array
, given an index (i.e. row number). Returns empty Array if the index is out of bounds.
Attributes
index
-
FixNum
indicating index of the row.
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# File 'lib/tablestakes.rb', line 94 def row(index) Array(get_row(index)) end |
#select(*columns) ⇒ Object Also known as: get_columns
Select columns from the table, given one or more column names. Returns an instance of Table
with the results. Raises ArgumentError if any column is not valid.
Attributes
columns
-
Variable
String
arguments to identify the columns to select
Examples
cities.select("City", "State") # returns a Table of "City" and "State" columns
cities.select(cities.headers) # returns a new Table that is a duplicate of cities
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# File 'lib/tablestakes.rb', line 357 def select(*columns) # check arguments raise ArgumentError, "Invalid column name(s)" unless columns columns.kind_of?(Array) ? columns.flatten! : nil columns.each do |c| raise ArgumentError, "Invalid column name" unless @table.has_key?(c) end result = [] result_headers = [] columns.each { |col| @headers.include?(col) ? result_headers << col : nil } result << result_headers @table[@headers.first].each_index do |index| this_row = [] result_headers.each do |col| this_row << @table[col][index] end result << this_row end result_headers.empty? ? Table.new() : Table.new(result) end |
#sort(column = nil, &block) ⇒ Object Also known as: sort!
Sort the table based on given column. Uses precedence as defined in the column. By default will sort by the value in the first column.
Attributes
args
-
OPTIONAL
String
to identify the column on which to sort
Options
datatype => :Fixnum
datatype => :Float
datatype => :Date
Examples
cities.sort("State") # Re-orders the cities table based on State name
cities.sort { |a,b| b<=>a } # Reverse the order of the cities table
cities.sort("State") { |a,b| b<=>a } # Sort by State in reverse alpha order
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# File 'lib/tablestakes.rb', line 555 def sort(column=nil, &block) col_index = 0 if column.kind_of? String col_index = @headers.index(column) elsif column.kind_of? Fixnum col_index = column end # return empty Table if empty if self.empty? return Table.new() end neworder = [] self.each { |row| neworder << OrderedRow.new(row,col_index) } result = [neworder.shift.data] # take off headers block_given? ? neworder.sort!(&block) : neworder.sort! neworder.each { |row| result << row.data } return Table.new(result) end |
#sub(colname, re = nil, replace = nil, &block) ⇒ Object
Given a field/column, and a regular expression to match against, and a replacement string, create a new table which performs a substitute operation on column data. In the case that the given replacement is a String
, a direct substitute is performed. In the case that it is a Hash
and the matched text is one of its keys, the corresponding Hash
value will be substituted.
Optionally takes a block containing an operation to perform on all matching data elements in the given column. Raises ArgumentError if the column is not found.
Attributes
colname
-
String
to identify the column to join on re
-
Regexp
to match the value in the selected column replace
-
OPTIONAL
String
orHash
to specify the replacement text for the givenRegexp
- &block
-
OPTIONAL block to execute against matching values
Examples
cities.sub("Population", /(.*?),(.*?)/, '\1\2') # eliminate commas
capitals.sub("State", /NY/, "New York") # replace acronym with full name
capitals.sub("State") { |state| state.downcase } # Lowercase for all values
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# File 'lib/tablestakes.rb', line 470 def sub(colname, re=nil, replace=nil, &block) # check arguments raise ArgumentError, "No regular expression to match against" unless re raise ArgumentError, "Invalid column name" unless @table.has_key?(colname) replace_str = "" if replace.respond_to?(:fetch) replace_str = replace.fetch(re) elsif replace.respond_to?(:to_str) replace_str = replace.to_str else raise ArgumentError, "Replacement must be String or Hash" end result = Table.new([@headers]) col_index = @headers.index(colname) self.each do |row| if block_given? row[col_index] = block.call row[col_index] else row[col_index] = row[col_index].sub(re, replace_str) end result.add_row(row) end return result end |
#tally(colname) ⇒ Object
Count instances in a particular field/column and return a Table
of the results. Raises ArgumentError if the column is not found.
Attributes
colname
-
String
to identify the column to tally
Examples
cities.tally("State") # returns each State in the cities Table with number of occurences
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# File 'lib/tablestakes.rb', line 336 def tally(colname) # check arguments raise ArgumentError, "Invalid column name" unless @table.has_key?(colname) result = {} @table[colname].each do |val| result.has_key?(val) ? result[val] += 1 : result[val] = 1 end return Table.new([[colname,"Count"]] + result.to_a) end |
#to_a ⇒ Object
Converts a Table
object to an array of arrays (each row). The first entry are the table headers.
Attributes
none
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# File 'lib/tablestakes.rb', line 239 def to_a result = [ Array(@headers) ] @table[@headers.first].each_index do |index| items = [] @headers.each do |col| items << @table[col][index] end result << items end result end |
#to_s ⇒ Object
Converts a Table
object to a tab-delimited string.
Attributes
none
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# File 'lib/tablestakes.rb', line 218 def to_s result = @headers.join("\t") << "\n" @table[@headers.first].each_index do |index| @headers.each do |col| result << @table[col][index].to_s unless col == @headers.last result << "\t" else result << "\n" end end end result end |
#top(colname, num = 1) ⇒ Object
Returns counts of the most frequent values found in a given column in the form of a Table. Raises ArgumentError if the column is not found. If no limit is given to the number of values, only the top value will be returned.
Attributes
colname
-
String
to identify the column to count num
-
OPTIONAL
String
number of values to return
Examples
cities.top("State") # returns a Table with the most frequent state in the cities Table
cities.top("State", 10) # returns a Table with the 10 most frequent states in the cities Table
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# File 'lib/tablestakes.rb', line 302 def top(colname, num=1) freq = tally(colname).to_a[1..-1].sort_by {|k,v| v }.reverse return Table.new(freq[0..num-1].unshift([colname,"Count"])) end |
#union(table2, colname, col2name = colname) ⇒ Object
Return Array with the union of elements columns in the given tables, eliminating duplicates. Raises an ArgumentError if a column is not found.
Attributes
table2
-
Table
to identify the secondary table in the union colname
-
String
to identify the column to union col2name
-
OPTIONAL
String
to identify the column in the second table to union
Examples
cities.union(capitals, "City", "Capital") # returns Array with all cities in both tables
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# File 'lib/tablestakes.rb', line 510 def union(table2, colname, col2name=colname) # check arguments raise ArgumentError, "Invalid table!" unless table2.is_a?(Table) raise ArgumentError, "Invalid column name" unless @table.has_key?(colname) raise ArgumentError, "Invalid column name" unless table2.headers.include?(col2name) return self.column(colname) | table2.column(col2name) end |
#where(colname, condition = nil) ⇒ Object Also known as: get_rows
Given a particular condition for a given column field/column, return a subtable that matches the condition. If no condition is given, a new Table
is returned with all records. Returns an empty table if the condition is not met or the column is not found.
Attributes
colname
-
String
to identify the column to tally condition
-
OPTIONAL
String
containing a ruby condition to evaluate
Examples
cities.where("State", "=='NY'") # returns a Table of cities in New York state
cities.where("State", "=~ /New.*/") # returns a Table of cities in states that start with "New"
cities.where("Population", ".to_i > 1000000") # returns a Table of cities with population over 1 million
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# File 'lib/tablestakes.rb', line 395 def where(colname, condition=nil) # check arguments raise ArgumentError, "Invalid Column Name" unless @headers.include?(colname) result = [] result << @headers self.each do |row| if condition eval(%q["#{row[headers.index(colname)]}"] << "#{condition}") ? result << row : nil else result << row end end result.length > 1 ? Table.new(result) : Table.new() end |
#write_file(filename) ⇒ Object
Write a representation of the Table
object to a file (tab delimited).
Attributes
filename
-
String
to identify the name of the file to write
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# File 'lib/tablestakes.rb', line 583 def write_file(filename) file = File.open(filename, "w") file.print self.to_s end |