Implemented Collection::reduce

Cake/Test/TestCase/Utility/CollectionTest.php

@@ -217,4 +217,28 @@ public function testMap() {
 		$this->assertInstanceOf('\Cake\Utility\Iterator\ReplaceIterator', $map);
 		$this->assertEquals(['a' => 1, 'b' => 4, 'c' => 9], iterator_to_array($map));
 	}
+
+/**
+ * Tests reduce
+ *
+ * @return void
+ */
+	public function testReduce() {
+		$items = ['a' => 1, 'b' => 2, 'c' => 3];
+		$collection = new Collection($items);
+		$callable = $this->getMock('stdClass', ['__invoke']);
+		$callable->expects($this->at(0))
+			->method('__invoke')
+			->with(10, 1, 'a')
+			->will($this->returnValue(11));
+		$callable->expects($this->at(1))
+			->method('__invoke')
+			->with(11, 2, 'b')
+			->will($this->returnValue(13));
+		$callable->expects($this->at(2))
+			->method('__invoke')
+			->with(13, 3, 'c')
+			->will($this->returnValue(16));
+		$this->assertEquals(16, $collection->reduce($callable, 10));
+	}
 }

Cake/Utility/Collection.php

@@ -223,6 +223,24 @@ public function map(callable $c) {
 		return new ReplaceIterator($this, $c);
 	}
 
+/**
+ * Folds the values in this collection to a single value, as the result of
+ * applying the callback function to all elements. $zero is the initial state
+ * of the reduction, and each successive step should of it should be returned
+ * by the callback function.
+ *
+ * The callback function is
+ *
+ * @return void
+ */
+	public function reduce(callable $c, $zero) {
+		$result = $zero;
+		foreach ($this as $k => $value) {
+			$result = $c($result, $value, $k);
+		}
+		return $result;
+	}
+
 	public function mapReduce(callable $map, callable $reduce) {
 	}