Add Enumerable#group_by and Array#in_groups_of

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@3726 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,30 @@
 *SVN*
 
+* Add Enumerable#group_by for grouping collections based on the result of some
+  block. Useful, for example, for grouping records by date.
+
+  ex.
+
+     latest_transcripts.group_by(&:day).each do |day, transcripts| 
+       p "#{day} -> #{transcripts.map(&:class) * ', '}"
+     end
+     "2006-03-01 -> Transcript"
+     "2006-02-28 -> Transcript"
+     "2006-02-27 -> Transcript, Transcript"
+     "2006-02-26 -> Transcript, Transcript"
+
+  Add Array#in_groups_of, for iterating over an array in groups of a certain
+  size.
+
+  ex.
+
+     %w(1 2 3 4 5 6 7).in_groups_of(3) {|g| p g}
+     ["1", "2", "3"]
+     ["4", "5", "6"]
+     ["7", nil, nil]
+
+  [Marcel Molina Jr., Sam Stephenson]
+
 * Added Kernel#daemonize to turn the current process into a daemon that can be killed with a TERM signal [DHH]
 
 * Add 'around' methods to Logger,  to make it easy to log before and after messages for a given block as requested in #3809. [Michael Koziarski]  Example:

activesupport/lib/active_support/core_ext/array.rb

@@ -2,4 +2,20 @@ require File.dirname(__FILE__) + '/array/conversions'
 
 class Array #:nodoc:
   include ActiveSupport::CoreExtensions::Array::Conversions
+
+  # Iterate over an array in groups of a certain size, padding any remaining 
+  # slots with specified value (<tt>nil</tt> by default).
+  # 
+  # E.g.
+  # 
+  #   %w(1 2 3 4 5 6 7).in_groups_of(3) {|g| p g}
+  #   ["1", "2", "3"]
+  #   ["4", "5", "6"]
+  #   ["7", nil, nil]
+  def in_groups_of(number, fill_with = nil, &block)
+    require 'enumerator'
+    collection = dup
+    collection << fill_with until collection.size.modulo(number).zero?
+    collection.each_slice(number, &block)
+  end
 end

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -6,4 +6,31 @@ module Enumerable #:nodoc:
     end
     match
   end
-end
+
+  # Collect an enumerable into sets, grouped by the result of a block. Useful,
+  # for example, for grouping records by date.
+  #
+  # e.g. 
+  #
+  #   latest_transcripts.group_by(&:day).each do |day, transcripts| 
+  #     p "#{day} -> #{transcripts.map(&:class) * ', '}"
+  #   end
+  #   "2006-03-01 -> Transcript"
+  #   "2006-02-28 -> Transcript"
+  #   "2006-02-27 -> Transcript, Transcript"
+  #   "2006-02-26 -> Transcript, Transcript"
+  #   "2006-02-25 -> Transcript"
+  #   "2006-02-24 -> Transcript, Transcript"
+  #   "2006-02-23 -> Transcript"
+  def group_by
+    inject([]) do |groups, element|
+      value = yield(element)
+      if (last_group = groups.last) && last_group.first == value
+        last_group.last << element
+      else
+        groups << [value, [element]]
+      end
+      groups
+    end
+  end
+end

activesupport/test/core_ext/array_ext_test.rb

@@ -34,3 +34,34 @@ class ArrayExtConversionTests < Test::Unit::TestCase
     assert_equal "one", ['one'].to_sentence
   end
 end
+
+class ArrayExtGroupingTests < Test::Unit::TestCase
+  def test_group_by_with_perfect_fit
+    groups = []
+    ('a'..'i').to_a.in_groups_of(3) do |group|
+      groups << group
+    end
+
+    assert_equal [%w(a b c), %w(d e f), %w(g h i)], groups
+  end
+
+  def test_group_by_with_padding
+    groups = []
+    ('a'..'g').to_a.in_groups_of(3) do |group|
+      groups << group
+    end
+
+    assert_equal [%w(a b c), %w(d e f), ['g', nil, nil]], groups
+  end
+
+  def test_group_by_pads_with_specified_values
+    groups = []
+
+    ('a'..'g').to_a.in_groups_of(3, false) do |group|
+      groups << group
+    end
+
+    assert_equal [%w(a b c), %w(d e f), ['g', false, false]], groups
+  end
+
+end

activesupport/test/core_ext/enumerable_test.rb

@@ -12,4 +12,19 @@ class EnumerableTests < Test::Unit::TestCase
     assert_equal true, (1..10).first_match {|x| x > 9}
     assert_equal :aba, {:a => 10, :aba => 50, :bac => 40}.first_match {|k, v| k if v > 45}
   end
-end
+
+  def test_group_by
+    names = %w(marcel sam david jeremy)
+    klass = Class.new
+    klass.send(:attr_accessor, :name)
+    objects = (1..50).inject([]) do |people,| 
+      p = klass.new
+      p.name = names.sort_by { rand }.first
+      people << p
+    end
+
+    objects.group_by {|object| object.name}.each do |name, group|
+      assert group.all? {|person| person.name == name}
+    end
+  end
+end