Added "compact" filter

lib/liquid/standardfilters.rb

@@ -165,6 +165,20 @@ module Liquid
         end
       end
     end
+    
+    # Remove nils within an array
+    # provide optional property with which to check for nil
+    def compact(input, property = nil)
+      ary = InputIterator.new(input)
+
+      if property.nil?
+        ary.compact
+      elsif ary.first.respond_to?(:[])
+        ary.reject{ |a| a[property].nil? }
+      elsif ary.first.respond_to?(property)
+        ary.reject { |a| a.send(property).nil? }
+      end
+    end
 
     # Replace occurrences of a string with another
     def replace(input, string, replacement = ''.freeze)
@@ -397,6 +411,10 @@ module Liquid
         to_a.uniq(&block)
       end
 
+      def compact
+        to_a.compact
+      end
+
       def each
         @input.each do |e|
           yield(e.respond_to?(:to_liquid) ? e.to_liquid : e)

test/integration/filter_test.rb

@@ -104,6 +104,27 @@ class FiltersTest < Minitest::Test
     assert_equal sorted[2].a, 'C'
   end
 
+  def test_compact
+    @context['words'] = ['a', nil, 'b', nil, 'c']
+    @context['hashes'] = [{ 'a' => 'A' }, { 'a' => nil }, { 'a' => 'C' }]
+    @context['objects'] = [TestObject.new('A'), TestObject.new(nil), TestObject.new('C')]
+
+    # Test strings
+    assert_equal ['a', 'b', 'c'], Variable.new("words | compact").render(@context)
+
+    # Test hashes
+    sorted = Variable.new("hashes | compact: 'a'").render(@context)
+    assert_equal sorted[0]['a'], 'A'
+    assert_equal sorted[1]['a'], 'C'
+    assert_nil sorted[2]
+
+    # Test objects
+    sorted = Variable.new("objects | compact: 'a'").render(@context)
+    assert_equal sorted[0].a, 'A'
+    assert_equal sorted[1].a, 'C'
+    assert_nil sorted[2]
+  end
+
   def test_strip_html
     @context['var'] = "<b>bla blub</a>"