Question

任何人都可以解释如何使用这个数组：

array(
    'Anto' => 25,
    'Filip' => 22,
    'Marko' => 17,
    'Josip' => 23,
    'Igor' => 24,
    'Ivan' => 23,
);

并将其映射为：

array(
    17 => [1, 'Marko'],
    22 => [1, 'Filip'],
    23 => [2, 'Josip', 'Ivan'],
    24 => [1, 'Igor'],
    25 => [1, 'Anto'],
);

新数组包含年龄（来自初始数组的值）的键，值是一个数组，其中包含具有相同年龄的人数，后跟所有具有相同年龄的名称。

Answer 1

foreach比array_map()更简单。我还利用array_key_exists()和ksort()来使事情更清洁。请参阅下面的文档示例。

<强> 实施例

// Data.
$initialArray = array(
    'Anto' => 25,
    'Filip' => 22,
    'Marko' => 17,
    'Josip' => 23,
    'Igor' => 24,
    'Ivan' => 23,
);
$newArray = array();

// Loop.
foreach($initialArray as $name => $age) {
    if(!array_key_exists($age, $newArray)) {
        // Initialize this age in the new array with empty counter.
        $newArray[$age] = array(0);
    }

    // Increment the counter.
    $newArray[$age][0]++;

    // Append the name.
    $newArray[$age][] = $name;
}

// Sort by age.
ksort($newArray);

// Dump.
print_r($newArray);

<强> 输出：

Array
(
    [17] => Array
        (
            [0] => 1
            [1] => Marko
        )

    [22] => Array
        (
            [0] => 1
            [1] => Filip
        )

    [23] => Array
        (
            [0] => 2
            [1] => Josip
            [2] => Ivan
        )

    [24] => Array
        (
            [0] => 1
            [1] => Igor
        )

    [25] => Array
        (
            [0] => 1
            [1] => Anto
        )

)

这只是众多方法之一。我强烈建议您更多地了解foreach控件结构，以便您完全掌握这个概念......作为程序员，它必须向前发展！

您也可以通过在逻辑结尾添加计数器来完成此操作。首先，您将根据其年龄对每个名称进行排序。然后，您将在count($names)索引处将$names添加到$age数组的开头。

Answer 2

您可以使用array_walk。你走了：

$array = [
    'John' => 25,
    'Tony' => 25,
    'Anto' => 25,
    'Filip' => 22,
    'Marko' => 17,
    'Josip' => 23,
    'Igor' => 24,
    'Ivan' => 23,
];

$ages = [];

array_walk($array, function ($age, $name) use (&$ages) {
    // Does the age already exist? If so, we'll increment
    // the count, otherwise we'll initialize it to one.
    array_key_exists($age, $ages) ? $ages[$age][0]++ : $ages[$age][0] = 1;

    $ages[$age][] = $name;
});

var_dump($ages);

输出：

array:5 [▼
  25 => array:4 [▼
    0 => 3
    1 => "John"
    2 => "Tony"
    3 => "Anto"
  ]
  22 => array:2 [▼
    0 => 1
    1 => "Filip"
  ]
  17 => array:2 [▼
    0 => 1
    1 => "Marko"
  ]
  23 => array:3 [▼
    0 => 2
    1 => "Josip"
    2 => "Ivan"
  ]
  24 => array:2 [▼
    0 => 1
    1 => "Igor"
  ]
]

如何使用array_map

2 个答案: