Online PHP editor | refs for cmH8P

<?php $arr = array ( Array ( "contact_id" => 5000, 'invoice' => 476 ), Array ( 'contact_id' => 5000, 'invoice' => 396 ), Array ( 'contact_id' => 1490, 'invoice' => 1083 ), Array ( 'contact_id' => 1490, 'invoice' => 498 )); $res =array(); Foreach($arr as $subarr){ Foreach($subarr as $key => $val){ If($key == "contact_id") { If(!isset($res[$val])) $res[$val] = array(); $cid = $val; }Else{ $res[$cid][]= $val; } } } Var_dump($res);