使用`array_map`和array_walk_recursive`轉換和重組多維數組

array_map用於創建新數組並轉換嵌套數據，需手動遞歸處理多維結構；array_walk_recursive用於直接修改葉節點值且支持鍵訪問，自動深入到最底層。 1. 使用array_map（配合遞歸函數）可對多維數組進行不可變轉換，適用於需要返回新數組的場景；2. 使用array_walk_recursive可原地修改字符串、數值等葉節點，適合執行日誌記錄、數據清洗等副作用操作；3. 當需同時調整結構與值時，可先遞歸重命名或重組鍵，再用array_walk_recursive處理值；4. 核心區別在於array_map返回新數組而array_walk_recursive修改原數組，選擇應基於是否需要保留原始數據。

When working with multidimensional arrays in PHP, you often need to transform or restructure nested data—whether it's sanitizing input, modifying values, renaming keys, or flattening structures. Two powerful functions that help with this are array_map and array_walk_recursive . While they may seem similar at first glance, they serve different purposes and are best used in specific scenarios.

Here's how to effectively use both to manipulate multidimensional arrays.

Using array_map for Transforming Nested Arrays

array_map applies a callback function to the elements of one or more arrays and returns a new array with the transformed values. When dealing with multidimensional arrays, you typically need to apply array_map recursively to reach deeper levels.

Example: Increment All Numeric Values in a Nested Array

 function deep_map($callback, $array) {
    $result = [];
    foreach ($array as $key => $value) {
        if (is_array($value)) {
            $result[$key] = deep_map($callback, $value); // Recurse into sub-arrays
        } else {
            $result[$key] = $callback($value);
        }
    }
    return $result;
}

$data = [
    'user1' => ['age' => 25, 'score' => 88],
    'user2' => ['age' => 30, 'score' => 92],
];

$incremented = deep_map(function($item) {
    return is_numeric($item) ? $item 1 : $item;
}, $data);

print_r($incremented);

Output:

 Array
(
    [user1] => Array
        (
            [age] => 26
            [score] => 89
        )
    [user2] => Array
        (
            [age] => 31
            [score] => 93
        )
)

✅ Use array_map (or a recursive wrapper) when you want to return a new transformed array without modifying the original.

Using array_walk_recursive for In-Place Modification

array_walk_recursive walks through every leaf node (non-array element) in a multidimensional array and applies a callback. It's ideal when you want to modify values directly or perform operations like validation or logging.

Unlike array_map , it doesn't return a new array—you modify values by reference.

Example: Convert All Strings to Uppercase

 $data = [
    'product' => [
        'name' => 'laptop',
        'category' => 'electronics',
        'tags' => ['gaming', 'portable']
    ],
    'location' => 'warehouse a'
];

array_walk_recursive($data, function(&$value, $key) {
    if (is_string($value)) {
        $value = strtoupper($value);
    }
});

print_r($data);

Output:

 Array
(
    [product] => Array
        (
            [name] => LAPTOP
            [category] => ELECTRONICS
            [tags] => Array
                (
                    [0] => GAMING
                    [1] => PORTABLE
                )
        )
    [location] => WAREHOUSE A
)

✅ Use array_walk_recursive when you want to modify leaf values in place or perform side effects (eg, logging, validation).

Key Differences Summary

When to Combine Both?

Sometimes you need structural changes and deep value transformation. In such cases, combining both approaches makes sense.

For example, renaming keys recursively while modifying values:

 function deep_transform(&$array) {
    foreach ($array as $key => $value) {
        // Rename keys
        if ($key === 'score') {
            $array['grade'] = $value;
            unset($array[$key]);
        }

        // Recurse into sub-arrays
        if (is_array($value)) {
            deep_transform($array[$key]);
        }
    }

    // Now modify scalar values
    array_walk_recursive($array, function(&$val) {
        if (is_string($val)) {
            $val = trim($val);
        }
    });
}

This hybrid approach gives full control over both structure and content.

Final Notes

• array_map is functional —it returns new data. Great for immutability.
• array_walk_recursive is imperative —it works on existing data. Efficient for bulk updates.
• Always consider whether you need a new array or can modify in place.
• Be cautious with references ( &$value ) to avoid unintended side effects.

Basically, choose based on your goal: transform → array_map , modify → array_walk_recursive .

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