Set#classify

set_classify.rb

#!/usr/bin/env ruby
# coding:utf-8

# = Summary:
#
# Set#classify Example.
#
# Returns Hash instance whose key is date, and value is the set object
# consist from date instances within from date_range's first date to 
# date_range's last date.
#

require 'date'
require 'set'
require 'pp'

# Set [START_DATE END_DATE]
date_range = %w[2012-08-01 2012-08-31]

Date.class_eval do
  def to_sdate
    Date::DAYNAMES[wday]
  end
end

# Make all target dates
dates = Range.new(*date_range.map(&Date.method(:parse))).to_a

# Main
pp Set.new(dates).classify(&:to_sdate)

# code which is not using Set#classify:
#   NOTE: returned hash's values are instance of Array 
#         while values are instance of Set using Set#classify.
#from_normal = dates.inject({}){|memo, d| memo.key?(d.to_sdate) ? memo[d.to_sdate] << d : memo[d.to_sdate] = [d]; memo }