Where do I create the array for a graph in an angular-codeigniter project

I have a project that uses Angular and Codeigniter. I have a graph which uses an array as input. I use the following code to build the array in Codeigniter controller:

function get_graph_data()
{
    $project_id = $this->site_settings->get_decrypt_id($this->input->post('project_id'));
    $year = ($this->input->post('year') ? $this->input->post('year') : date('Y'));
    $result = $this->Income_expense_model->get_graph_data($project_id, $year);
    for ($i = 1; $i <= 12; $i++) {
        $dummy_date = strtotime("1991-" . $i . "-13");
        $month_name = date('F', $dummy_date);
        $array['months'][$i] = $month_name;
        $array['income'][$i] = "0";
        $array['expense'][$i] = "0";
    }

    foreach($result as $row) {
        if ($row->type == 1) $array['income'][$row->month_num] = $row->amount;
        else $array['expense'][$row->month_num] = $row->amount;
    }

    $data['months'] = array_values($array['months']);
    $data['income'] = array_values($array['income']);
    $data['expense'] = array_values($array['expense']);
    echo json_encode($data);
}

I use a service to get this array from my Angular controller and uses it there.
Am I doing the right thing? Where should I build the array?
1. In the Codeigniter controller like I did
or
2. By getting just the
$result = $this->Income_expense_model->get_graph_data($project_id, $year);
array which is not formatted from the Codeigniter controller and building it in the Angular controller?
or something else?