PHP array_filter, how to get the key in callback?

From the documentation:PHP 5.6.0 Added optional flag parameter and constants ARRAY_FILTER_USE_KEY and ARRAY_FILTER_USE_BOTH

http://php.net/manual/en/function.array-filter.php

In a previous comment you outlined you're actually looking for something like this:

foreach ($t as $k => $v)    if (!array_key_exists($k, $valid))        unset($t[$k])

So actually to remove all values from array $t that do not have a key in array $valid.

The PHP function for that is called array_intersect_key. The intersection is equal to the filtered result:

$filtered = array_intersect_key($t, $valid);

There's no way to let the callback of array_filter access the element's key, nor is there a similar function that does what you want.

However, you can write your own function for this, like the one below:

function arrayfilter(array $array, callable $callback = null) {    if ($callback == null) {        $callback = function($key, $val) {            return (bool) $val;        };    }    $return = array();    foreach ($array as $key => $val) {        if ($callback($key, $val)) {            $return[$key] = $val;        }    }    return $return;}$test_array = array('foo', 'a' => 'the a', 'b' => 'the b', 11 => 1101, '', null, false, 0);$array = arrayfilter($test_array, function($key, $val) {   return is_string($key);});print_r($array);/*Array(    [a] => the a    [b] => the b)*/$array = arrayfilter($test_array);print_r($array);/*Array(    [0] => foo    [a] => the a    [b] => the b    [11] => 1101)*/