diff --git a/app/Http/Controllers/DeviceController.php b/app/Http/Controllers/DeviceController.php
index b0513be..266a422 100644
--- a/app/Http/Controllers/DeviceController.php
+++ b/app/Http/Controllers/DeviceController.php
@@ -308,6 +308,7 @@ class DeviceController extends Controller
         if($modelQuery){
             $datalist = $modelQuery->where('device_id', $deviceId)->get()->keyBy('monitored_at')->toArray();
         }
+        $data = [];
         foreach ($getArr as $column){
             $data[$column] = [];
             foreach($xKeys as $key){