Description:
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---
From manual page: http://www.php.net/function.preg-grep
---
I'm asking for an extra flag to this function, to cause it to do its search in the array keys rather than in the values.

While there's a comment in the above page of how to "post-process" preg_grep() results to achieve this, I'd rather it be done in C (inside the PCRE code) than PHP for performance reasons.

I thought about something like this:
$a = array_flip( preg_grep('/Version$/', array_flip($aParams)) );

which would almost return what I want, HOWEVER it has two problems:
1) If certain values of $aParams are duplicated, the first array_flip() will "lose" those rows in the array.
2) I'd incur a sizeable CPU and memory hit by calling array_flip, which duplicates the array(s) in RAM.


Test script:
---------------
The current work-around:

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;
}