- var_dump: documentation ( source)
- array_reduce: documentation ( source)
<?php
$arr = array(0 => array("key" => "val"), 1 => array("key" => "anotherval"));
$key = "key";
$result = array_reduce($arr, function(&$cur, $item) use ($key)
{
return $cur=array_key_exists($key, $item)?$cur[]=$item[$key]:$cur;
}, []);
var_dump($result);