How to get a subset of $_POST array with keys starting with a prefix

Question

Let's say my $_POST variable looks like:

<?php

Array
(
    [user_ID] => 65
    [action] => editpost
    [originalaction] => editpost
    [post_author] => 154
    [empl_bd_dd] => 6
    [empl_bd_mm] => 5
    [empl_bd_yy] => 1987
    [empl_gen] => 1
    [empl_height] => 155
    [empl_weight] => 61
    [empl_arra] => 2
    [save] => Update
    [post_it] => 2
    [empl_pay] => J77
    [empl_cust] => Married
    [empl_lang] => Array
        (
            [0] => EN
            [1] => FR
        )
    [empl_rent] => 1
    [name] => Jimmy Nathan
    [empl_text] => Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec sed interdum leo. Sed et elit quam, tempor placerat neque. Nullam sapien odio, egestas iaculis dictum ut, congue ullamcorper tellus.
    [empl_sk_0] => 6
    [empl_sk_1] => 7
    [empl_sk_2] => 5
)

?>

As you can see I prefixed all my form variables with empl_. Short of having to specify all of them one by one, how do I get all my form variables from $_POST into an array in the least-cost hopefully elegant way? Is there a PHP array function or a combination of them that I can use for this?

Like in CSS where you can select all elements with a class that starts with empl using [class*="empl_"], is there a way I can do this with the array keys in PHP, e.g.

$empl_post = $_POST['empl_*']

---

EDITED ANSWER - impt correction to @chris 's answer: $_POST has to be the first argument to array_intersect_key, e.g.:

$empl_POST = array_intersect_key($_POST, array_flip(preg_grep('/^empl_/', array_keys($_POST))));

Answer 1

$r = array_intersect_key($_POST, array_flip(preg_grep('/^empl_/', array_keys($_POST))));

_{they really need to add a PREG_GREP_KEYS flag to preg_grep() so we don't have to do all that mess...}

As a function:

function preg_grep_keys($pattern, $input, $flags = 0) {
    return array_intersect_key(
        $input,
        array_flip(preg_grep(
           $pattern,
           array_keys($input),
           $flags
        ))
    );
}

Edit - since php 5.6 array_filter now has some new flags that let you access the array key in the filter callback.

function preg_grep_keys($pattern, $input, $flags = 0) {
    return array_filter($input, function($key) use ($pattern, $flags) {
           return preg_match($pattern, $key, $flags);
    }, ARRAY_FILTER_USE_KEY);
}

use

$filtered = preg_grep_keys('/^empl_/', $_POST);

Answer 2

function GetPrefixedItemsFromArray($array, $prefix)
{
    $keys = array_keys($array);
    $result = array();

    foreach ($keys as $key)
    {
        if (strpos($key, $prefix) === 0)
        {
            $result[$key] = $array[$key];
        }
    }

    return $result;
}

Then simply call with $myArray = GetPrefixedItemsFromArray($_POST, "empl_");.

Answer 3

$empl_post = array();
foreach ($_POST as $k => $v) {
    if (strpos($k, 'empl_') !== 0) continue;
    $empl_post[substr($k, 5)] = $v
}

print_r($empl_post);