A shorter way to run a match on the array's keys rather than the values:

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

Run a match on the array's keys rather than the values:

<?php

function preg_grep_keys( $pattern, $input, $flags = 0 )
{
    $keys = preg_grep( $pattern, array_keys( $input ), $flags );
    $vals = array();
    foreach ( $keys as $key )
    {
        $vals[$key] = $input[$key];
    }
    return $vals;
}

?>

This may be obvious to most experienced developers,but just in case its not,when using preg_grep to check for whitelisted items ,one must be very careful to explicitly define the regex boundaries or it will fail
<?php
$whitelist = ["home","dashboard","profile","group"];
$possibleUserInputs = ["homd","hom","ashboard","settings","group"];
foreach($possibleUserInputs as  $input)
{
     if(preg_grep("/$input/i",$whitelist)
    {
         echo $input." whitelisted";
    }else{
         echo $input." flawed";
    }

}
?>
This results in:

homd flawed
hom whitelisted
ashboard whitelisted
settings flawed
group whitelisted

I think this is because if boundaries are not explicitly defined,preg_grep looks for any instance of  the substring in the whole array and returns true if found.This is not what we want,so boundaries must be defined.

<?php
foreach($possibleUserInputs as  $input)
{
     if(preg_grep("/^$input$/i",$whitelist)
    {
         echo $input." whitelisted";
    }else{
         echo $input." flawed";
    }

}
?>
this results in:
homd flawed
hom flawed
ashboard flawed
settings flawed
group whitelisted
in_array() will also give the latter results but will require few tweaks if say,the search is to be case insensitive,which is always the case 70% of the time