Unable to pass array data from view to controller using AJAX

The data (array of array) is not getting passed from view to controller while using AJAX in CodeIgniter (PHP)

url is working in $.ajax. It is redirecting to the method in controller

view.php (view)

$('#save').click(function(){
    var table_data = [];

    // use .each to get all data
    $('#data_table tr').each(function(row,tr){

        // create array again to store data by row
        // get only data with value 

        if ($(tr).find('td:eq(0)').text() == "") {
        } else {
        var sub = {
            'no' : $(tr).find('td:eq(0)').text(),
            'firstname' : $(tr).find('td:eq(1)').text(),
            'middle' : $(tr).find('td:eq(2)').text(),
            'last' : $(tr).find('td:eq(3)').text(),
        };

        table_data.push(sub);
    }
});

//use ajax to insert the data

console.log(table_data); 

var data = {'data_table':table_data};

console.log(data);

 $.ajax({
    data : data,
    type : 'POST',
    url : 'save',
    crossOrigin : false,
    dataType : 'array',
    success: function(msg){
        $('.answer').html(msg);
     }

}); 

Welcome.php (controller)

public function save() {

    $relatives_list = $this->input->post('data'); 
    echo 'as';

    echo $relatives_list; 
    // the list is not shown here

    $this->load->model('Batch');
    $status = $this->Batch->save($relatives_list);

    $this->output->set_content_type('application/json');
    echo json_encode(array('status' => $status)); 
}

Batch.php (model)

 public function save($relative_list){
$length = count($relative_list);

    for($x = 0; $x < count($relative_list); $x++){
        $data[] = array(
            'no' => $relative_list[$x]['no'],
            'firstname' => $relative_list[$x]['firstname'],
            'middle' => $relative_list[$x]['middle'],
            'last' => $relative_list[$x]['last'],

        );
    }
    try {


        for($x = 0; $x<count($relative_list); $x++){
            $this->db->insert('hhh',$data[$x]);
        }
        return 'success';
    }catch(Exception $e) {
         return 'failed';
    }

}

Error:

parameter-must-be-an-array-or-an-object-that-implements-countable