Copying x random values from one array to another PHP

Question

I'm trying to copy 5 random values from one array to another with the following code. The problem is 3 or 4 values get copied and 1 or 2 are always copied as null. I'm not sure what the problem in my code is.

if (count($potential_matches_in_area) >= 5) {
  for ($x = 0; $x < 5; $x++) {

  $index = mt_rand(0, count($potential_matches_in_area) - 1);
  $new_matches[$x] = $potential_matches_in_area[$index];
  unset($potential_matches_in_area[$index]);

  }

Kevin · Accepted Answer · 2016-06-07 22:57:32Z

1

The problem is, this line:

mt_rand(0, count($potential_matches_in_area) - 1);

You can get duplicate keys, the first time it runs, it runs okay, but once the unset key reappears again, you'll get an undefined index. Why not just use array_rand instead.

if (count($potential_matches_in_area) >= 5) {
    for ($x = 0; $x < 5; $x++) {
        $index = array_rand($potential_matches_in_area);
        $new_matches[$x] = $potential_matches_in_area[$index];
        unset($potential_matches_in_area[$index]);
    } 
}

You'll only get the present keys thats still available.

answered Jun 7, 2016 at 22:57

Kevin

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2 Comments

Alk Over a year ago

I've read that array_rand is less efficient and has some issues with the distribution producing weird results occasionally, however if it is the only way, I will use it

Kevin Over a year ago

@mankee if you want to insist your mt_rand, you'll need to roll up your own custom function that utilizes mt_rand and then corresponds to your array

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