php array filter syntax

<?php

$arr = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4];

var_dump(array_filter($arr, function($k) {
    return $k == 'b';
}, ARRAY_FILTER_USE_KEY));

var_dump(array_filter($arr, function($v, $k) {
    return $k == 'b' || $v == 4;
}, ARRAY_FILTER_USE_BOTH));
?>

$numbers = [2, 4, 6, 8, 10];

function MyFunction($number)
{
  return $number > 5;
}

$filteredArray = array_filter($numbers, "MyFunction");

/**
 * `$filteredArray` now contains: `[6, 8, 10]`
 * NB: Use this to remove what you don't want in the array
 * @see `array_map` when you want to alter/change elements
 * in the array.
 */

$numbers = [-2, 4, -6, 8, 10];

function isPositive($number)
{
  return $number > 0;
}

$filteredArray = array_filter($numbers, "isPositive");