Question

I’m trying to make a function that is able to rotate through an array a given amount of times and then return the first index. But what I have is really slow and clunky. Take a look:

<?php

/**
 * Get the current userid
 * @return integer
 */
public function getCurrentUser( DateTime $startDate, DateInterval $interval, DateTime $endDate, $currentUser, $users, $rotating )
{

    if ($rotating == 0)
    {
        return $currentUser;
    }

    $usrArray = array();
    $dateRange = new DatePeriod( $startDate, $interval, $endDate);

    // Push userIds to an array
    foreach ($users as $user)
    {
        $usrArray[] = $user->id;
    }

    // Get the number of iterations from startDate to endDate
    $steps = iterator_count($dateRange);

    // Find the initial position of the orignal user
    $key = array_search($currentUser, $usrArray);

    // Set up the array so index 0 == currentUser
    $usr = $usrArray;
    array_splice($usr, $key);
    $slice = array_slice($usrArray, $key);
    $startList = array_merge($slice, $usr);

    // Start rotating the array
    for ($i=0; $i < $steps; $i++)
    {
        array_push($startList, array_shift($startList));
    }

    return $startList[0];
}

Here’s an Xdebug profile before the PHP script timed out.
xdebug profile

Is there a better way to figure out who is index 0 after x amount of rotations?

Answer 1

Your array rotation is not that slow but it can be improved .. i believe this is your rotation code

Your code

// Start rotating the array
for ($i=0; $i < $steps; $i++)
{
    array_push($startList, array_shift($startList));
}

return $startList[0];

You can remove the loop replace it with mod .. the way you can still get the same results here is the solution:

Solution

return $startList[ $steps % count($startList)];

You would get the same result .

Simple benchmark & Testing

$steps = 10000; <----------------- 10,000 steps 

set_time_limit(0);
echo "<pre>";
$file = "log.txt";
// Using your current code
function m1($steps) {
    $startList = range("A", "H");
    for($i = 0; $i < $steps; $i ++) {
        array_push($startList, array_shift($startList));
    }
    return $startList[0];
}

// Using InfiniteIterator
function m2($steps) {
    $startList = range("A", "H");
    $n = 0;
    foreach ( new InfiniteIterator(new ArrayIterator($startList)) as $l ) {
        if ($n == $steps) {
            return $l;
            break;
        }
        $n ++;
    }
}

// Simple MOD solution
function m3($steps) {
    $startList = range("A", "H");
    return $startList[ $steps % count($startList)];
}

$result = array('m1' => 0,'m2' => 0,'m3' => 0);

for($i = 0; $i < 1; ++ $i) {
    foreach ( array_keys($result) as $key ) {
        $alpha = microtime(true);
        $key($file);
        $result[$key] += microtime(true) - $alpha;
    }
}

echo '<pre>';
echo "Single Run\n";
print_r($result);
var_dump(m1($steps),m2($steps),m2($steps));
echo '</pre>';

Output

Single Run
Array
(
    [m1] => 0.00012588500976562
    [m2] => 0.00021791458129883
    [m3] => 7.7962875366211E-5   <----------------- Mod solution fastest 
)
string 'A' (length=1)               |
string 'A' (length=1)               |+------------- They all return same result
string 'A' (length=1)               |