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

Question

Let\'s say my $_POST variable looks like:

 65
    [action] => editpost
    [originalaction] => editpo         


        

Answer 1

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

print_r($empl_post);

Answer 2

Another method:

$formVars = $_POST;
foreach ($formVars as $key=>$value) {
    if (strpos($key, 'empl_')===false) 
        unset($formVars[$key]);
}

Answer 3

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 4

Here's a cool ultra-php-neat way to use php array_walk to specify a generic prefix to remove:

$foo = array('k_foo' =>"bar", 
              'k_bar' =>"b0r", 
              'y_foo' =>"b5r",
              'y_not' =>"b7r", 
             'k_not' =>"b1r");

$subsetArray = $foo;
$key_prefix = "k_";

array_walk($foo, 'removeUnwanted', array(&$subsetArray, $key_prefix));
var_dump ($subsetArray);

function removeUnwanted($value, $key, $array){
    $prefix = $array[1];
    $testArray = &$array[0];
    if(strpos($key,$prefix) ===0){
        unset($testArray[$key]); 
    } 
}

Now you can just call array walk, with a copy of the array of values, and the prefix string.

Answer 5

If you want something like this

$keyPattern = '/^empl_*/';
$matching_array = getArrayElementsWithMatchingKeyPattern($_POST,$keyPattern);

Then I dont think there is an inbuilt way to that. Best way would be a foreach loop with a regex match.

function getArrayElementsWithMatchingKeyPattern($array,$keyPattern){
    $matching_array = array();

    foreach ($keyPattern as $k => $v) {
       if (preg_match($array[$k],$keyPattern) > 0)
             $matching_array[$k] = $v;
    }

    return ($matching_array);

}

Answer 6

$r = array_intersect_key($_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);