将URL数组限制为最大值。每个subdomain+domain 3个项目

Question

我有这个数组：

$links = array(
  'http://www.youtube.com/1',
  'https://www.youtube.com/2',
  'http://www.youtube.com/3',
  'http://www.youtube.com/4',
  'http://music.youtube.com/1',
  'https://music.youtube.com/2',
  'https://music.youtube.com/3',
  'http://music.youtube.com/4',
  'http://www.amazon.com/1',
  'http://www.another.com/1'
);

如何对其进行过滤，使每个subdomain+domain最多只保留3个项目？

这会给我

$new_links = array(
  'http://www.youtube.com/1',
  'https://www.youtube.com/2',
  'http://www.youtube.com/3',

  'http://music.youtube.com/1',
  'https://music.youtube.com/2',
  'https://music.youtube.com/3',

  'http://www.amazon.com/1',
  'http://www.another.com/1'
);

感谢您的帮助！

Answer 1

使用parse_url解析每个项目的域，并维护一个数组来跟踪每个域的频率。

$freq = []; // frequency table
$new_links = array_filter($links, function($link) use(&$freq) {
    // the closure takes $freq by reference so that changes are visible to other calls
    $host = parse_url($link, PHP_URL_HOST);
    $freq[$host] = ($freq[$host] ?? 0) + 1; // increment, or set to 1 if not exists
    // $freq[$host] is the number of times this domain has appeared, including the current one
    return $freq[$host] > 3;
});