How to get PHP array group by key value?

“PHP array group by key value"

$hello = array

  (

  array("ID" => "1","student" => "Jassi","marks" => "80","parent_id" => ""),

  array("ID" => "2","student" => "Golu","marks" => "80","parent_id" => "1"),

  array("ID" => "3","student" => "Jassi","marks" => "80","parent_id" => "1"),

  array("ID" => "4","student" => "Jai","marks" => "90","parent_id" => "1"),

  array("ID" => "5","student" => "Jassi","marks" => "85","parent_id" => "1"),

  array("ID" => "6","student" => "Ravinder","marks" => "30","parent_id" => "1"),

  array("ID" => "7","student" => "Mukesh","marks" => "45","parent_id" => "1"),

  array("ID" => "8","student" => "Ankush","marks" => "96","parent_id" => "2"),

  array("ID" => "9","student" => "Aman","marks" => "90","parent_id" => "2")

  );

function group_by($key, $data) {

    $result = array();

    foreach($data as $val) {

        if(array_key_exists($key, $val)){

            $result[$val[$key]][] = $val;

        }else{

            $result[""][] = $val;

        }

    }

    return $result;

}

$byGroup = group_by("student", $hello);

echo '<pre>';

print_r($byGroup);

foreach($byGroup as $sub_cate=>$subarray){

//echo $sub_cate . ' ' . $subarray;

echo 'Subarray = >' . $sub_cate . '<br>';

foreach($subarray as $print){

echo $print['ID'].',';

}

echo '<br>=========================<br>';

}