## mapToGroups 方法通過給定的回調函數對集合項進行分組。該回調函數應該返回一個包含單個鍵 / 值對的關聯數組，從而生成一個分組值的新集合 mapToGroups 方法通過給定的回調函數對集合項進行分組。該回調函數應該返回一個包含單個鍵 / 值對的關聯數組，從而生成一個分組值的新集合： ``` $collection = collect([ [ 'name' => 'John Doe', 'department' => 'Sales', ], [ 'name' => 'Jane Doe', 'department' => 'Sales', ], [ 'name' => 'Johnny Doe', 'department' => 'Marketing', ] ]); $grouped = $collection->mapToGroups(function ($item, $key) { return [$item['department'] => $item['name']]; }); $grouped->all(); /* [ 'Sales' => ['John Doe', 'Jane Doe'], 'Marketing' => ['Johnny Doe'], ] */ $grouped->get('Sales')->all(); // ['John Doe', 'Jane Doe'] ```