multidemensial_array.php

<?php
  $domains = [
    0 => [
      'domain_id' => 7,
    ],
    1 => [
      'domain_id' => 7,
    ],
    2 => [
      'domain_id' => 7,
    ],
    3 => [
      'domain_id' => 7,
    ],
    // ... This but 8189 more times.
  ];

  // Method 1.
  $time = -microtime(TRUE);
  $correct_domains = array_unique($domains);
  $time += microtime(TRUE);
  echo "Deduped to " . count($correct_domains) . " in " . $time . "seconds.";
  // Deduped to 80 in 160.97429418564 seconds.


  // Method 2.
  $time = -microtime(TRUE);
  $correct_domains2 = [];
  foreach ($domains as $key => $domain) {
    $correct_domains2[$domain] = TRUE;
  }
  $correct_domains2 = array_keys($correct_domains2);
  $time += microtime(TRUE);
  echo "deduped to " . count($correct_domains2) . " in " . $time . "seconds.";
  // Deduped to 80 in 7.2383348941803 seconds.