How to get unique value in multidimensional array

Question

I have done a lot of looking around on the overflow, and on google, but none of the results works for my specific case.

I have a placeholder array called $holder, va

Answer 1

Just iterate over it and apply an array_unique on the result:

foreach($holder as $yourValues){
    $pids[] = $yourValues['pid'];
}
$yourUniquePids = array_unique($pids);

Answer 2

In php >= 5.5 you can use array_column:

array_unique(array_column($holder, 'pid'));