Performance Improvement: Alternative for array_flip function.

Question

Is there any way I can avoid using array_flip to optimize performance. I am doing a select statement from database, preparing the query and executing it and storing data as an associative array in $resultCollection and than I have array op and for each element in $resultCollection am storing its outputId in op[] as evident from the code.

I have explained code and so my question is how can I achieve an similar alternative for array_flip with using array_flip as I want to improve performance.

$resultCollection = $statement->fetchAll(PDO::FETCH_ASSOC);

$op = array();

//Looping through result collection and storing unicaOfferId into op array. 
foreach ($resultCollection as $output)
{
$op[] = $output['outputId'];
}

//Here op array has key as 0, 1, 2...and value as id {which I am interested in}

//Flip op array to get offer ids as key

$op = array_flip($op);

//Doing a flip to get id as key. 

foreach ($ft as $Id => $Off)
{
    $ft[$Id]['is_set'] = isset($op[$Id]);
}

Answer 1

Well, since it doesn't look like you care about the value, bur rather just the O(1) lookup speed of the keys, I'd build the $op that way the first time

foreach ($resultCollection as $output)
{
  $op[$output['outputId']] = null;
}

Or you can look into in_array(), I don't know how its speed compares. (Seems like this is 0(n), so not faster)

EDIT

If you wanted to create the first time around what you were getting after array_flip(), do it this way.

$i = 0;
foreach ($resultCollection as $output)
{
  $op[$output['outputId']] = $i++;
}

But after your comments, I'm still not sure if I really "get" what you're after.

Answer 2

You should be able to use the key from the foreach for indexes and build the array pre-flipped like this.

    foreach ($resultCollection as $key => $output) {
        $op[ $output['outputId'] ] = $key;
    }