指定したキーで配列をグルーピングする

gistfile1.txt

class KeyGrouper{
    public static function group($records, $keys){                                              
        $groupedRecords = array();                                                              
        foreach($records as $record){                                                           
            $primaryKeyString = KeyGrouper::primaryKeyString($record, $keys);                   
            $groupedRecords[$primaryKeyString][] = $record;                                     
        }                                                                                       
        return $groupedRecords;                                                                 
    }       
                
    private static function primaryKeyString($record, $keys){                                   
        $str = array();
        foreach($keys as $key){                                                                 
            $str[] = "{$key}:{$record[$key]}";                                                  
        }                                                                                       
        return implode("_", $str);                                                              
    }                                                                                           
}