Question

I have an array that is given to me in random order. The array is an array of arrays, and I am given an order to place the array in based on a key that exists in each sub-array.

For example, I am given the array array(array('id' => 1), array('id' => 2)). I am told to order the arrays in the order (2,1) based upon the key ‘id’ of each sub-array.

What is the most efficient way to do this in PHP?

Answer 1

PHP does allow you to write your own sort functions. I can’t vouch for the efficiency of this solution, but it will work and is supported by the language directly, so I like it.

For your case you would write something like this:

function custom_sort_by_id($a, $b) {
    // If the two IDs are the same, no sorting should be done
    if ($a['id'] == $b['id']) {
     return 0;
    }

    return ($a['id'] < $b['id']) ? -1 : 1;
}

You would then call this function as follows:

usort($myarray, "custom_sort_by_id");

So, if for example you have the following starting array:

array(3) {
  [0]=>
  array(2) {
    ["id"]=>        int(3)
    ["value"]=>     int(1)
  }
  [1]=>
  array(2) {
    ["id"]=>        int(2)
    ["value"]=>     int(2)
  }
  [2]=>
  array(2) {
    ["id"]=>        int(1)
    ["value"]=>     int(3)
  }
}

You’ll receive the following result:

array(3) {
  [0]=>
  array(2) {
    ["id"]=>        int(1)
    ["value"]=>     int(3)
  }
  [1]=>
  array(2) {
    ["id"]=>        int(2)
    ["value"]=>     int(2)
  }
  [2]=>
  array(2) {
    ["id"]=>        int(3)
    ["value"]=>     int(1)
  }
}