- var_dump: documentation ( source)
- array_merge: documentation ( source)
- sort: documentation ( source)
- array_unique: documentation ( source)
<?php
$oldArray = [["2"],["2","3","4"],["8","9"],["7","4"]];
$newArray = array_unique(call_user_func_array('array_merge', $oldArray));
sort($newArray);
var_dump($newArray);