Query Count Monthly of this year - Laravel 5.8

Today is 9/25/2019

I'm trying to query my visitor with in this year of 2019 only.

Then, I want to know how many are on

1,2,3,4,5,6,7,8,9

I've tried

$raw = Visitor::query()
->whereYear('created_at', now()->year -1)
->get()
->pluck('created_at');

$data = [];
foreach ($raw as $i=>$date) {
    $data[$i] = Carbon::parse($date)->format('m');
    if(  Carbon::parse($date)->format('m')[0] != 0 ){
        $data[$i] = Carbon::parse($date)->format('m');
    }else{
        $data[$i] = str_replace('0','',Carbon::parse($date)->format('m'));
    }
}

// dd($data);

$dataValues = array_count_values($data);

dd($dataValues);

I got

array:5 [▼
  8 => 314
  9 => 916
  10 => 764
  11 => 827
  12 => 765
]

Why would I get anything in the future since this month is only September (9) ?

Please help me correct it.

I was hoping to get sth like this

array:9 [▼
      0 => 314
      1 => 916
      2 => 764
      3 => 827
      4 => 165
      5 => 225
      6 => 565
      7 => 65
      8 => 1265

    ]

via Chebli Mohamed