PHP 根据key 给二维数组分组

为了根据key给二维数组分组，我们可以使用PHP的array_reduce()函数。

具体步骤如下：

1.定义一个空数组，用于存储结果；

2.使用array_reduce()函数遍历二维数组；

3.判断当前数组元素key值是否存在于结果数组中，如果存在，则将该元素push进对应的子数组；如果不存在，则创建该key对应的子数组并push元素进去；

4.最终返回结果数组。

以下是示例代码：

$arr = array(
    array('name' => 'John', 'age' => 21, 'gender' => 'male'),
    array('name' => 'Jane', 'age' => 25, 'gender' => 'female'),
    array('name' => 'Bob', 'age' => 22, 'gender' => 'male'),
    array('name' => 'Alice', 'age' => 27, 'gender' => 'female'),
    array('name' => 'Mark', 'age' => 23, 'gender' => 'male'),
    array('name' => 'Lisa', 'age' => 28, 'gender' => 'female')
);

$res = array_reduce($arr, function($carry, $item){
    $key = $item['gender'];
    isset($carry[$key]) ? array_push($carry[$key], $item) : $carry[$key] = array($item);
    return $carry;
}, array());

print_r($res);

以上代码将根据gender键值，将原始数组分组为两个子数组，其中一个包含所有female的元素，另一个包含所有male的元素。输出结果为：

Array
(
    [male] => Array
        (
            [0] => Array
                (
                    [name] => John
                    [age] => 21
                    [gender] => male
                )

            [1] => Array
                (
                    [name] => Bob
                    [age] => 22
                    [gender] => male
                )

            [2] => Array
                (
                    [name] => Mark
                    [age] => 23
                    [gender] => male
                )

        )

    [female] => Array
        (
            [0] => Array
                (
                    [name] => Jane
                    [age] => 25
                    [gender] => female
                )

            [1] => Array
                (
                    [name] => Alice
                    [age] => 27
                    [gender] => female
                )

            [2] => Array
                (
                    [name] => Lisa
                    [age] => 28
                    [gender] => female
                )

        )

)

以下是另一个示例，它根据age键值将数组分为3个子数组，分别存储小于20岁的人、20岁到25岁的人、以及25岁以上的人：

$arr = array(
    array('name' => 'John', 'age' => 21, 'gender' => 'male'),
    array('name' => 'Jane', 'age' => 25, 'gender' => 'female'),
    array('name' => 'Bob', 'age' => 22, 'gender' => 'male'),
    array('name' => 'Alice', 'age' => 27, 'gender' => 'female'),
    array('name' => 'Mark', 'age' => 23, 'gender' => 'male'),
    array('name' => 'Lisa', 'age' => 28, 'gender' => 'female'),
    array('name' => 'Tom', 'age' => 18, 'gender' => 'male'),
    array('name' => 'Lucy', 'age' => 19, 'gender' => 'female'),
    array('name' => 'Jack', 'age' => 30, 'gender' => 'male')
);

$res = array_reduce($arr, function($carry, $item){
    $key = $item['age'] < 20 ? 'young' : ($item['age'] < 25 ? 'middle' : 'old');
    isset($carry[$key]) ? array_push($carry[$key], $item) : $carry[$key] = array($item); 
    return $carry;
}, array());

print_r($res);

以上代码将根据age键值，将原始数组分为3个子数组，其中一个包含所有小于20岁的元素，另一个包含所有20岁到25岁的元素，第三个包含所有25岁以上的元素。输出结果为：

Array
(
    [middle] => Array
        (
            [0] => Array
                (
                    [name] => John
                    [age] => 21
                    [gender] => male
                )

            [1] => Array
                (
                    [name] => Bob
                    [age] => 22
                    [gender] => male
                )

            [2] => Array
                (
                    [name] => Mark
                    [age] => 23
                    [gender] => male
                )

        )

    [old] => Array
        (
            [0] => Array
                (
                    [name] => Alice
                    [age] => 27
                    [gender] => female
                )

            [1] => Array
                (
                    [name] => Lisa
                    [age] => 28
                    [gender] => female
                )

            [2] => Array
                (
                    [name] => Jack
                    [age] => 30
                    [gender] => male
                )

        )

    [young] => Array
        (
            [0] => Array
                (
                    [name] => Tom
                    [age] => 18
                    [gender] => male
                )

            [1] => Array
                (
                    [name] => Lucy
                    [age] => 19
                    [gender] => female
                )

        )

)