Group array values based on key in php?

Question

I have a array like this:

$str=
   Array
(
    [No] => 101
    [Paper_id] => WE3P-1
    [Title] => \"a1\"
    [Author] => ABC
    [Aff_list] =>         


        

Answer 1

Thanks to crater and Fabio's answer. I updated the code to check if the size of the key is not greater than one (1), underscore will not be appended.

function _group_by($array, $keys=array()) {
    $return = array();
    $append = (sizeof($keys) > 1 ? "_" : null);
    foreach($array as $val){
        $final_key = "";
        foreach($keys as $theKey){
            $final_key .= $val[$theKey] . $append;
        }
        $return[$final_key][] = $val;
    }
    return $return;
}