# groupBy方法 根据给定的键对集合内的项目进行分组。 ``` $collection = collect([ ['account_id' => 'account-x10', 'product' => 'Chair'], ['account_id' => 'account-x10', 'product' => 'Bookcase'], ['account_id' => 'account-x11', 'product' => 'Desk'], ]); $grouped = $collection->groupBy('account_id'); $grouped->toArray(); /* [ 'account-x10' => [ ['account_id' => 'account-x10', 'product' => 'Chair'], ['account_id' => 'account-x10', 'product' => 'Bookcase'], ], 'account-x11' => [ ['account_id' => 'account-x11', 'product' => 'Desk'], ], ] */ ``` 除了传入一个字符串的「键」，还可以传入一个回调。该回调应该返回用来分组的键的值。 ``` $grouped = $collection->groupBy(function ($item, $key) { return substr($item['account_id'], -3); }); $grouped->toArray(); /* [ 'x10' => [ ['account_id' => 'account-x10', 'product' => 'Chair'], ['account_id' => 'account-x10', 'product' => 'Bookcase'], ], 'x11' => [ ['account_id' => 'account-x11', 'product' => 'Desk'], ], ] */ ```