Implemented Collection::indexBy

Cake/Test/TestCase/Utility/CollectionTest.php

@@ -368,5 +368,51 @@ public function testGroupByDeepKey() {
 		$this->assertEquals($expected, iterator_to_array($grouped));
 	}
 
+/**
+ * Tests indexBy
+ *
+ * @return void
+ */
+	public function testIndexBy() {
+		$items = [
+			['id' => 1, 'name' => 'foo', 'parent_id' => 10],
+			['id' => 2, 'name' => 'bar', 'parent_id' => 11],
+			['id' => 3, 'name' => 'baz', 'parent_id' => 10],
+		];
+		$collection = new Collection($items);
+		$grouped = $collection->indexBy('id');
+		$expected = [
+			1 => ['id' => 1, 'name' => 'foo', 'parent_id' => 10],
+			3 => ['id' => 3, 'name' => 'baz', 'parent_id' => 10],
+			2 => ['id' => 2, 'name' => 'bar', 'parent_id' => 11],
+		];
+		$this->assertEquals($expected, iterator_to_array($grouped));
+		$this->assertInstanceOf('\Cake\Utility\Collection', $grouped);
+
+		$grouped = $collection->indexBy(function($element) {
+			return $element['id'];
+		});
+		$this->assertEquals($expected, iterator_to_array($grouped));
+	}
+
+/**
+ * Tests indexBy with a deep property
+ *
+ * @return void
+ */
+	public function testIndexByDeep() {
+		$items = [
+			['id' => 1, 'name' => 'foo', 'thing' => ['parent_id' => 10]],
+			['id' => 2, 'name' => 'bar', 'thing' => ['parent_id' => 11]],
+			['id' => 3, 'name' => 'baz', 'thing' => ['parent_id' => 10]],
+		];
+		$collection = new Collection($items);
+		$grouped = $collection->indexBy('thing.parent_id');
+		$expected = [
+			10 => ['id' => 3, 'name' => 'baz', 'thing' => ['parent_id' => 10]],
+			11 => ['id' => 2, 'name' => 'bar', 'thing' => ['parent_id' => 11]],
+		];
+		$this->assertEquals($expected, iterator_to_array($grouped));
+	}
 
 }

Cake/Test/TestCase/Utility/MapReduceTest.php

@@ -84,7 +84,7 @@ public function testEmitFinalInMapper() {
 	}
 
 /**
- * Tests that a reducer is required when there are intermediate resutls
+ * Tests that a reducer is required when there are intermediate results
  *
  * @expectedException \LogicException
  * @return void

Cake/Utility/Collection.php

@@ -420,7 +420,50 @@ public function groupBy($callback) {
 		return new self($group);
 	}
 
-	public function indexBy($property) {
+/**
+ * Given a list, and an callback function that returns a key for each element
+ * in the list (or a property name) returns an object with an index of each item.
+ * Just like groupBy, but for when you know your keys are unique.
+ *
+ * When $callback is a string it should be a property name to extract or
+ * a dot separated path of properties that should be followed to get the last
+ * one in the path.
+ *
+ * ###Example:
+ *
+ * {{{
+ * $items = [
+ *	['id' => 1, 'name' => 'foo'],
+ *	['id' => 2, 'name' => 'bar'],
+ *	['id' => 3, 'name' => 'baz'],
+ * ];
+ *
+ * $indexed = (new Collection($items))->indexBy('id');
+ *
+ * //Or
+ * $indexed = (new Collection($items))->indexBy(function($e) {
+ *	return $e['id'];
+ * });
+ *
+ * //Result will look like
+ * [
+ *	1 => ['id' => 1, 'name' => 'foo'],
+ *	3 => ['id' => 3, 'name' => 'baz'],
+ *	2 => ['id' => 2, 'name' => 'bar'],
+ * ];
+ * }}}
+ *
+ * @param callable|string the callback or column name to use for indexing
+ * or a function returning the indexing key out of the provided element
+ * @return \Cake\Utility\Collection
+ */
+	public function indexBy($callback) {
+		$callback = $this->_propertyExtractor($callback);
+		$group = [];
+		foreach ($this as $value) {
+			$group[$callback($value)] = $value;
+		}
+		return new self($group);
 	}
 
 	public function countBy($property) {