Update item_property to recognize integers

lib/jekyll/filters.rb

@@ -371,10 +371,15 @@ def item_property(item, property)
     # rubocop:disable Performance/RegexpMatch
     # return numeric values as numbers for proper sorting
     def parse_sort_input(property)
-      number_like = %r!\A\s*-?(?:\d+\.?\d*|\.\d+)\s*\Z!
-      return property.to_f if property.to_s =~ number_like
-
-      property
+      float_like = %r!\A\s*-?(?:\d+\.?\d*|\.\d+)\s*\Z!
+      integer_like = %r!\A\s*-?\d+\s*\Z!
+      if property.to_s =~ integer_like
+        property.to_i
+      elsif property.to_s =~ float_like
+        property.to_f
+      else
+        property
+      end
     end
     # rubocop:enable Performance/RegexpMatch
 

test/test_filters.rb

@@ -831,6 +831,16 @@ def to_liquid
           )
         end
       end
+
+      should "should pass integers as is" do
+        grouping = @filter.group_by([
+          {"name" => "Allison", "year" => 2016},
+          {"name" => "Amy", "year" => 2016},
+          {"name" => "George", "year" => 2019},
+        ], "year")
+        assert_equal "2016", grouping[0]["name"]
+        assert_equal "2019", grouping[1]["name"]
+      end
     end
 
     context "where filter" do