Inefficient rotating of an array - php

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) |