计算多维数组中的值

Question

我目前有以下数组:

Array(
        [0] => Array
            (
                [user] => Name 1
                [group] => 1
            )
        [1] => Array
            (
                [user] => Name 2
                [group] => 1
            )
        [2] => Array
            (
                [user] => Name 3
                [group] => 2
            )
        [3] => Array
            (
                [user] => Name 4
                [group] => 2
            )
        [4] => Array
            (
                [user] => Name 5
                [group] => 3
            )
)

我正在尝试使用各种group值作为键创建一个新数组,然后计算每组中有多少以提供以下内容:

Array
(
    [1] => 2
    [2] => 2
    [3] => 1
)

我试图使用以下内容,但是我收到了未定义的索引警告:

$newArr = array();
foreach ($details['user_groups'] as $key => $value) {
        $newArr[$value['user_groups']]++;
}

(我确实检查了SO的其他答案,但找不到试图做同样的事情)

Answer 1

这可以通过简单的迭代完成:

$counts = array();
foreach ($array as $key=>$subarr) {
  // Add to the current group count if it exists
  if (isset($counts[$subarr['group']]) {
    $counts[$subarr['group']]++;
  }
  // or initialize to 1 if it doesn't exist
  else $counts[$subarr['group']] = 1;

  // Or the ternary one-liner version 
  // instead of the preceding if/else block
  $counts[$subarr['group']] = isset($counts[$subarr['group']]) ? $counts[$subarr['group']]++ : 1;
}

PHP 5.5的更新

在PHP 5.5中,它添加了array_column()从2D数组聚合内部键的功能,这可以简化为:

$counts = array_count_values(array_flip(array_column($array, 'group')));

Answer 2

这可以通过一个简单的array_map功能来完成

$array = array_map(function($element){
    return $element['group'];
}, $array1);

$array2 = (array_count_values($array));

print_r($array2);