Formating JSON from Laravel Eloquent Response

I have a response from Eloquent and i need to format it exactly as followed :

{
    name: "James",
    data: {
      "2017-01-01 00:00:00": 300,
      "2017-01-02 00:00:00": 600,
    }
  },

The current response i am getting is :

{
name: "James",
date: "2017-01-01 00:00:00",
amount: "300"
},
{
name: "James",
date: "2017-01-02 00:00:00",
amount: "600"
},

I have tied this, but the format is not correct :

 $chartData = [];

    foreach($charts as $chart){

        array_push($chartData, [
            'name' => $chart->name,
            'data' => json_encode([$chart->date. ':' .$chart->amount], true)
        ]);

    }

Result is :

{
name: "James",
data: "{"2017-01-01T00:00:00.000000Z":"300"}"
},
{
name: "James",
data: "{"2017-01-02T00:00:00.000000Z":"600"}"
},

Thanks

via Chebli Mohamed