sample_array_reduce.php

<?php
$a = array('name' => array( 'error1', 'error2'));
$b = array('email' => array('error3', 'error4'));
$errors = array_merge($a, $b);


$result = array_reduce($errors, function($c, $v) { return array_merge($c, $v); }, array());
print_r($errors);
print_r($result);
print_r(implode('\n', $result));

Array
(
    [name] => Array
        (
            [0] => error1
            [1] => error2
        )

    [email] => Array
        (
            [0] => error3
            [1] => error4
        )

)
Array
(
    [0] => error1
    [1] => error2
    [2] => error3
    [3] => error4
)
error1\nerror2\nerror3\nerror4