php数组group by

在 PHP 中，可以使用 array_reduce() 函数来实现类似于 SQL 的 GROUP BY 功能，以下是一个示例代码：

<?php
$data = array(
    array('name' => 'John', 'age' => 25, 'gender' => 'male'),
    array('name' => 'Jane', 'age' => 22, 'gender' => 'female'),
    array('name' => 'Bob', 'age' => 30, 'gender' => 'male'),
    array('name' => 'Alice', 'age' => 28, 'gender' => 'female'),
    array('name' => 'Tom', 'age' => 25, 'gender' => 'male')
);

$grouped = array_reduce($data, function($result, $item) {
    $key = $item['age'];
    if (!isset($result[$key])) {
        $result[$key] = array();
    }
    $result[$key][] = $item;
    return $result;
}, array());

print_r($grouped);
?>

上述代码将按照年龄将数组 $data 中的元素进行分组，输出结果如下：

Array
(
    [25] => Array
        (
            [0] => Array
                (
                    [name] => John
                    [age] => 25
                    [gender] => male
                )

            [1] => Array
                (
                    [name] => Tom
                    [age] => 25
                    [gender] => male
                )

        )

    [22] => Array
        (
            [0] => Array
                (
                    [name] => Jane
                    [age] => 22
                    [gender] => female
                )

        )

    [30] => Array
        (
            [0] => Array
                (
                    [name] => Bob
                    [age] => 30
                    [gender] => male
                )

        )

    [28] => Array
        (
            [0] => Array
                (
                    [name] => Alice
                    [age] => 28
                    [gender] => female
                )

        )

)

可以看到，输出结果是一个关联数组，其中键值为分组的依据（这里是年龄），对应的值为分组后的元素数组。