PHP quickly gets random small arrays in large arrays

There is a function to guess what users like. Users can refresh the recommended content by clicking to change a group.

First query the database to get the first 1000 pieces of data, and then randomly remove 4 pieces.

After I finished writing the program, I found that it ran very slowly. Every time I refreshed it, I had to wait a long time for it to come out.

The code is as follows:

$arr = range(1, 100000);
$start = time();
for($i = 0; $i < 100; $i ++){
    $key = mt_rand(0, 99999 - $i);
    $result[] = $arr[$key];
    unset($arr[$key]);
    sort($arr);
}
$end = time();
echo $end - $start;

The above writing method must be sorted after using unset.

unset will only delete the key value, but the key will be retained.

The improved writing method is as follows:

$arr = range(1, 100000);
$start = time();
for($i = 0; $i < 100; $i ++){
    $key = mt_rand(0, 99999 - $i); 
    $result[] = array_splice($arr, $key, 1);
}
$end = time();
echo $end - $start;

The efficiency has increased by 3-4 times.