When dealing with PHP multi-dimensional array deduplication, you cannot use array_unique directly, and other methods are required. 1. Use serialize and unserialize to combine array_map to serialize the sub-array into a string and then deduplicate it, and then restore it to an array, which is suitable for two-dimensional arrays; 2. Customize the comparison function arrayUnique, which manually compares each element through traversal, which is highly flexible but less efficient; 3. Note that the key names and order will affect the uniqueness judgment, and it is recommended to unify the structure or compare according to specific fields; 4. If deduplicate based on a certain field (such as id), you can use a temporary array to record the existing field values, and only the items that appear for the first time are retained. The selection method should be determined based on the data structure and performance requirements.

To deal with the problem of deduplication of PHP multi-dimensional arrays, it is actually not possible to solve the problem of using array_unique like one-dimensional arrays. Because elements of multidimensional arrays may be arrays, PHP default functions do not support comparisons of nested structures. However, as long as you master the correct method, it can still be achieved.

1. Use serialize and unserialize to cooperate with array_map

This is one of the most common solutions. The core idea is to first "serialize" each subarray into a string, so that you can compare it with array_unique .

 $uniqueArray = array_map('unserialize', array_unique(array_map('serialize', $originalArray)));

• serialize : converts each subarray into a string for easy comparison.
• array_unique : Remove duplicate strings.
• unserialize : Return to the array structure.

This method is suitable for two-dimensional arrays. If your array is deeper, it may require recursive processing.

2. Custom comparison function: use us_array_unique (manual traversal)

If you want to control the comparison method more flexibly, or if you want to support more complex structures, you can write a function yourself to compare one by one:

 function arrayUnique($array) {
    $result = [];
    foreach ($array as $item) {
        $found = false;
        foreach ($result as $existing) {
            if ($item === $existing) {
                $found = true;
                break;
            }
        }
        if (!$found) {
            $result[] = $item;
        }
    }
    return $result;
}

Although this method is not as efficient as built-in functions, it is better to be intuitive and controllable. For example, you can make unique judgments based on a certain field instead of exactly matching the entire subarray.

3. Note: Key names and order will also affect uniqueness judgment

What many people ignore is that even if the content of the two subarrays is the same, but the key names or orders are different, they will be regarded as different arrays . For example:

 ['a' => 1, 'b' => 2] !== ['b' => 2, 'a' => 1]

Therefore, before deduplication, it is best to unify the structure of the array, such as sorting first and then comparing, or only comparing specific fields.

4. What if you just deduplicate based on a certain field?

Sometimes you don't want to compare the entire line, but just want to keep unique items based on a certain field (such as id). This can be done at this time:

 $ids = [];
$result = [];

foreach ($originalArray as $item) {
    if (!in_array($item['id'], $ids)) {
        $result[] = $item;
        $ids[] = $item['id'];
    }
}

This method is especially suitable for deduplication by pressing the primary key from the data read from the database.

Basically these common methods. Which one you choose depends on your data structure and performance requirements. If it is a small amount of data, you can choose any one of them. If the array is large or the structure is complex, it is recommended to give priority to high-efficiency methods.

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