按子数组值对数组进行分组

Question

我有一个以下格式的子数组：

array
(
    a => array ( id = 20, name = chimpanzee )
    b => array ( id = 40, name = meeting )
    c => array ( id = 20, name = dynasty )
    d => array ( id = 50, name = chocolate )
    e => array ( id = 10, name = bananas )
    f => array ( id = 50, name = fantasy )
    g => array ( id = 50, name = football )
)

我想根据每个子数组中的 id 字段将它分组到一个新数组中。

array
(
    10 => array
          (
            e => array ( id = 10, name = bananas )
          )
    20 => array
          (
            a => array ( id = 20, name = chimpanzee )
            c => array ( id = 20, name = dynasty )
          )
    40 => array
          (
            b => array ( id = 40, name = meeting )
          )
    50 => array
          (
            d => array ( id = 50, name = chocolate )
            f => array ( id = 50, name = fantasy )
            g => array ( id = 50, name = football )
          )
)

Answer 1

$arr = array();

foreach ($old_arr as $key => $item) {
   $arr[$item['id']][$key] = $item;
}

ksort($arr, SORT_NUMERIC);

Answer 2

foreach($array as $key => $value){
   $newarray[$value['id']][$key] = $value;
}

var_dump($newarray);

小菜一碟；）

Answer 3

如果内部数组之一不包含 id，则以下代码改编 @Tim Cooper 的代码以减轻 Undefined index: id 错误：

$arr = array();

foreach($old_arr as $key => $item)
{
    if(array_key_exists('id', $item))
        $arr[$item['id']][$key] = $item;
}

ksort($arr, SORT_NUMERIC);

但是，它会删除没有 id 的内部数组。

例如

$old_arr = array(
    'a' => array ( 'id' => 20, 'name' => 'chimpanzee' ),
    'b' => array ( 'id' => 40, 'name' => 'meeting' ),
    'c' => array ( 'id' => 20, 'name' => 'dynasty' ),
    'd' => array ( 'id' => 50, 'name' => 'chocolate' ),
    'e' => array ( 'id' => 10, 'name' => 'bananas' ),
    'f' => array ( 'id' => 50, 'name' => 'fantasy' ),
    'g' => array ( 'id' => 50, 'name' => 'football' ),
    'h' => array ( 'name' => 'bob' )
);

将完全删除 'h' 数组。

Answer 4

你也可以从ouzo-goodies使用Arrays::groupBy()：

$groupBy = Arrays::groupBy($array, Functions::extract()->id);

print_r($groupBy);

结果：

Array
(
    [20] => Array
        (
            [0] => Array
                (
                    [id] => 20
                    [name] => chimpanzee
                )

            [1] => Array
                (
                    [id] => 20
                    [name] => dynasty
                )

        )

    [40] => Array
        (
            [0] => Array
                (
                    [id] => 40
                    [name] => meeting
                )

        )

    [50] => Array
        (
            [0] => Array
                (
                    [id] => 50
                    [name] => chocolate
                )

            [1] => Array
                (
                    [id] => 50
                    [name] => fantasy
                )

            [2] => Array
                (
                    [id] => 50
                    [name] => football
                )

        )

    [10] => Array
        (
            [0] => Array
                (
                    [id] => 10
                    [name] => bananas
                )

        )

)

这里是Arrays 和Functions 的文档。

Answer 5

这是一个函数，它将一个数组作为第一个参数，将一个条件（字符串或回调函数）作为第二个参数。该函数返回一个新数组，该数组根据要求对数组进行分组。

/**
 * Group items from an array together by some criteria or value.
 *
 * @param  $arr array The array to group items from
 * @param  $criteria string|callable The key to group by or a function the returns a key to group by.
 * @return array
 *
 */
function groupBy($arr, $criteria): array
{
    return array_reduce($arr, function($accumulator, $item) use ($criteria) {
        $key = (is_callable($criteria)) ? $criteria($item) : $item[$criteria];
        if (!array_key_exists($key, $accumulator)) {
            $accumulator[$key] = [];
        }

        array_push($accumulator[$key], $item);
        return $accumulator;
    }, []);
}

这是给定的数组：

$arr = array(
    'a' => array ( 'id' => 20, 'name' => 'chimpanzee' ),
    'b' => array ( 'id' => 40, 'name' => 'meeting' ),
    'c' => array ( 'id' => 20, 'name' => 'dynasty' ),
    'd' => array ( 'id' => 50, 'name' => 'chocolate' ),
    'e' => array ( 'id' => 10, 'name' => 'bananas' ),
    'f' => array ( 'id' => 50, 'name' => 'fantasy' ),
    'g' => array ( 'id' => 50, 'name' => 'football' )
);

以及使用带有字符串和回调函数的函数的示例：

$q = groupBy($arr, 'id');
print_r($q);

$r = groupBy($arr, function($item) {
    return $item['id'];
});
print_r($r);

两个例子的结果是一样的：

Array
(
    [20] => Array
        (
            [0] => Array
                (
                    [id] => 20
                    [name] => chimpanzee
                )

            [1] => Array
                (
                    [id] => 20
                    [name] => dynasty
                )

        )

    [40] => Array
        (
            [0] => Array
                (
                    [id] => 40
                    [name] => meeting
                )

        )

    [50] => Array
        (
            [0] => Array
                (
                    [id] => 50
                    [name] => chocolate
                )

            [1] => Array
                (
                    [id] => 50
                    [name] => fantasy
                )

            [2] => Array
                (
                    [id] => 50
                    [name] => football
                )

        )

    [10] => Array
        (
            [0] => Array
                (
                    [id] => 10
                    [name] => bananas
                )

        )

)

在上面的例子中传递回调是多余的，但是当你传入一个对象数组、多维数组或有一些你想要分组的任意东西时，使用回调就可以了。