Merge pull request #7 from fuadsaud/enumerable-frequency

Add Enumerable#frequency

README.md

@@ -27,6 +27,7 @@ Or install it yourself as:
 * [Enumerable](http://rdoc.info/github/bbatsov/powerpack/Enumerable)
     * [#drop_last](http://rdoc.info/github/bbatsov/powerpack/Enumerable#drop_last-instance_method)
     * [#drop_last_while](http://rdoc.info/github/bbatsov/powerpack/Enumerable#drop_last_while-instance_method)
+    * [#frequencies](http://rdoc.info/github/bbatsov/powerpack/Enumerable#frequencies-instance_method)
     * [#several?](http://rdoc.info/github/bbatsov/powerpack/Enumerable#several?-instance_method)
     * [#sproduct](http://rdoc.info/github/bbatsov/powerpack/Enumerable#sproduct?-instance_method)
     * [#sum](http://rdoc.info/github/bbatsov/powerpack/Enumerable#sum-instance_method)

lib/powerpack/enumerable.rb

@@ -1,5 +1,6 @@
 require_relative 'enumerable/drop_last'
 require_relative 'enumerable/drop_last_while'
+require_relative 'enumerable/frequencies'
 require_relative 'enumerable/several'
 require_relative 'enumerable/sproduct'
 require_relative 'enumerable/sum'

lib/powerpack/enumerable/frequencies.rb

@@ -0,0 +1,19 @@
+unless Enumerable.method_defined? :frequencies
+  module Enumerable
+    # Counts the number of ocurrence of items in the enumberable.
+    #
+    # @return [Hash] in the format value => count
+    #
+    # @example
+    #   [].frequency # => {}
+    #   [1, :symbol, 'string', 3, :symbol, 1].frequency
+    #     #=> { 1 => 2, :symbol => 2, 'string' => 1, 3 => 1 }
+    #
+    #
+    def frequencies
+      inject(Hash.new(0)) do |a, e|
+        a.tap { |acc| acc[e] += 1 }
+      end
+    end
+  end
+end

spec/powerpack/enumerable/frequencies_spec.rb

@@ -0,0 +1,20 @@
+require 'spec_helper'
+
+describe 'Enumerable#frequencies' do
+  context 'empty collection' do
+    it 'evaluates to an empty hash' do
+      expect([].frequencies).to eql({})
+    end
+  end
+
+  context 'populated collection' do
+    it 'counts the number of ocurrences and returns a hash in the form value => count' do
+      expect([1, 1, :symbol, 3, 1, :symbol, 'string'].frequencies).to eql(
+        1        => 3,
+        3        => 1,
+        'string' => 1,
+        :symbol  => 2
+      )
+    end
+  end
+end