add where filter to filter arrays of objects

lib/jekyll/filters.rb

@@ -158,7 +158,6 @@ module Jekyll
       input.to_json
     end
 
-
     # Group an array of items by a property
     #
     # input - the inputted Enumerable
@@ -179,6 +178,18 @@ module Jekyll
       end
     end
 
+    # Filter an array of objects
+    #
+    # input - the object array
+    # key - key within each object to filter by
+    # value - desired value
+    #
+    # Returns the filtered array of objects
+    def where(input, key, value)
+      return input unless input.class == Array
+      input.select { |object| object[key] == value }
+    end
+
     private
     def time(input)
       case input

test/test_filters.rb

@@ -16,6 +16,11 @@ class TestFilters < Test::Unit::TestCase
       @filter = JekyllFilter.new({"source" => source_dir, "destination" => dest_dir})
       @sample_time = Time.utc(2013, 03, 27, 11, 22, 33)
       @time_as_string = "September 11, 2001 12:46:30 -0000"
+      @array_of_objects = [
+        { "color" => "red",  "size" => "large"  },
+        { "color" => "red",  "size" => "medium" },
+        { "color" => "blue", "size" => "medium" }
+      ]
     end
 
     should "textilize with simple string" do
@@ -109,6 +114,11 @@ class TestFilters < Test::Unit::TestCase
         assert_equal "[1,2]", @filter.jsonify([1, 2])
         assert_equal "[{\"name\":\"Jack\"},{\"name\":\"Smith\"}]", @filter.jsonify([{:name => 'Jack'}, {:name => 'Smith'}])
       end
+
+      should "proper filter objects using where" do
+        assert_equal "some string", @filter.where("some string", nil, nil)
+        assert_equal 2, @filter.where(@array_of_objects, "color", "red").length
+      end
     end
 
     context "group_by filter" do