如何对包含对象的三维数组进行排序？

I'm building a WordPress site where I need to sort the results of a WP_User_Query AFTER the query has already been run. For those of you not familiar, it has elements that look like this:

Array (
  [0] => WP_User Object (
    [data] => stdClass Object (
      [ID] => 1
      [user_login] => MarvinLazer
      [user_pass] => $P$BUGHRCjMzlvn7dlGp53UTPC8GMF081/
      [user_nicename] => marvinlazer
      [user_email] => marvin@lazer.com
      [user_url] => http://marvinlazer.com
      [user_registered] => 2017-03-04 23:08:08
      [user_activation_key] =>
      [user_status] => 0
      [display_name] => Marvin Lazer
    )
    [ID] => 1
    [caps] => Array (
      [subscriber] => 1
    )
    [cap_key] => wp_capabilities
    [roles] => Array (
      [0] => subscriber
    )
    [allcaps] => Array (
      [read] => 1
      [level_0] => 1
      [subscriber] => 1
    )
    [filter] =>
  )
  [1] => WP_User Object ( etc. etc.

Based on this very helpful page on PHP array sorting, I feel like I got something kinda close. Unfortunately, it's just giving me a blank page after the part where the code appears.

          function cmp(array $a, array $b) {
              if ($a['data']['display_name'] < $b['data']['display_name']) {
                  return -1;
              } else if ($a['data']['display_name'] > $b['data']['display_name']) {
                  return 1;
              } else {
                  return 0;
              }
          }

          usort($user_query->results, 'cmp');

Anyone wanna point me towards what I'm doing wrong?

It's because you are trying to access property of object in method of accessing array element. You cannot use the index to access the property of object. You should use -> instead of []. You can check this demo to issustrate how to access object property.

refer to how to access array/object

change your $a['data']['display_name'] to $a->data->display_name, and your $b in the compare funciton.