Create a mapToGroups method (#18949)

Author: JosephSilber

src/Illuminate/Support/Collection.php

@@ -704,6 +704,25 @@ public function map(callable $callback)
         return new static(array_combine($keys, $items));
     }
 
+    /**
+     * Run a grouping map over the items.
+     *
+     * The callback should return an associative array with a single key/value pair.
+     *
+     * @param  callable  $callback
+     * @return static
+     */
+    public function mapToGroups(callable $callback)
+    {
+        $groups = $this->map($callback)->reduce(function ($groups, $pair) {
+            $groups[key($pair)][] = reset($pair);
+
+            return $groups;
+        }, []);
+
+        return (new static($groups))->map([$this, 'make']);
+    }
+
     /**
      * Run an associative map over each of the items.
      *

tests/Support/SupportCollectionTest.php

@@ -1049,6 +1049,35 @@ public function testFlatMap()
         $this->assertEquals(['programming', 'basketball', 'music', 'powerlifting'], $data->all());
     }
 
+    public function testMapToGroups()
+    {
+        $data = new Collection([
+            ['id' => 1, 'name' => 'A'],
+            ['id' => 2, 'name' => 'B'],
+            ['id' => 3, 'name' => 'C'],
+            ['id' => 4, 'name' => 'B'],
+        ]);
+
+        $groups = $data->mapToGroups(function ($item, $key) {
+            return [$item['name'] => $item['id']];
+        });
+
+        $this->assertInstanceOf(Collection::class, $groups);
+        $this->assertEquals(['A' => [1], 'B' => [2, 4], 'C' => [3]], $groups->toArray());
+        $this->assertInstanceOf(Collection::class, $groups['A']);
+    }
+
+    public function testMapToGroupsWithNumericKeys()
+    {
+        $data = new Collection([1, 2, 3, 2, 1]);
+
+        $groups = $data->mapToGroups(function ($item, $key) {
+            return [$item => $key];
+        });
+
+        $this->assertEquals([1 => [0, 4], 2 => [1, 3], 3 => [2]], $groups->toArray());
+    }
+
     public function testMapWithKeys()
     {
         $data = new Collection([