Online PHP editor | refs for oHsOk

<?php $data = [ [ 'blah' => 'reference', ], [ 'A' => 'SMI13', 'B' => '03/12/1940', 'C' => '', ] ]; foreach($data as &$record){ foreach($record as $key => $val){ //you might want to consider using preg_replace_callback instead: if(preg_match("/^(((0[13578]|1[02])\/(0[1-9]|[12]\d|3[01])\/((19|[2-9]\d)\d{2}))|((0[13456789]|1[012])\/(0[1-9]|[12]\d|30)\/((19|[2-9]\d)\d{2}))|(02\/(0[1-9]|1\d|2[0-8])\/((19|[2-9]\d)\d{2}))|(02\/29\/((1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|((16|[2468][048]|[3579][26])00))))$/",$val)) { echo "match! $val \n"; $record [$key] = date("Y-m-d", strtotime($val)); } } } unset($record); var_dump($data);