To remove duplicate values ??in PHP arrays, the most direct way is to use the array_unique function, which will retain the first occurrence of elements and remove subsequent duplicate values, such as $array = [1, 2, 2, 3, 4, 4, 4]; $uniqueArray = array_unique($array); The result is [1, 2, 3, 4]. If you want to re-index the array, you can use it with the array_values ??function; for multi-dimensional arrays or deduplication based on specific fields, it is necessary to manually control it. The common practice is to traverse the array and save the unique judgment field to a temporary array, and skip it when encountering duplication; in addition, you need to pay attention to order preservation, case processing and performance issues, especially in large data volumes, associative arrays should be optimized for search efficiency.

Deduplication is a common requirement when dealing with PHP arrays. If you want to know how to remove duplicate values ??from arrays, the method is actually not complicated. PHP has provided built-in functions to help you complete this task.

Use the array_unique function to quickly dereload

This is the most direct way. array_unique() function will iterate over the array and remove duplicate values. It retains the elements that appear for the first time, and subsequent duplications will be removed.

 $array = [1, 2, 2, 3, 4, 4, 4];
$uniqueArray = array_unique($array);

In this way $uniqueArray becomes [1, 2, 3, 4] . Note: This function will retain the key names of the original array. If you want to re-index the array, you can use array_values() together:

 $uniqueArray = array_values(array_unique($array));

This approach is suitable for most cases, but it should be noted that if an array contains incomparable types (such as objects), the results may not be as expected.

Handle multi-dimensional arrays or more complex structures

If you are facing a multi-dimensional array, or if you want to deduplicate based on a certain field (for example, the array is user information, and you want to deduplicate according to the user's ID), then you have to control it manually.

A common practice is to traverse the array and save the fields that judge uniqueness into a temporary array. If you encounter duplication, you will skip:

 $uniqueIds = [];
$result = [];

foreach ($users as $user) {
    if (!in_array($user['id'], $uniqueIds)) {
        $uniqueIds[] = $user['id'];
        $result[] = $user;
    }
}

The meaning of this code is: every time you take a user, check whether his ID has been added, and the final result will be added if it has not been added. Although this method is a little more written, it is more flexible and suitable for various custom conditions.

Notes and performance considerations

• Keep order : array_unique() retains the first occurrence of element positions by default. If you need other sorting methods, you may need to call sort() or usort() additionally.
• Case sensitive : For strings, the default is case sensitive. If you want to ignore upper and lower case, you can convert it to lower case before processing and then compare.
• Performance issues : For very large arrays, in_array() is less efficient in loops. You can use associative arrays to simulate sets to improve search speed:

 $seen = [];
foreach ($items as $item) {
    if (!isset($seen[$item])) {
        $seen[$item] = true;
        // Add results}
}

Basically that's it. Deduplication operation seems simple, but there are still some details that need to be paid attention to in actual development, especially when the data volume is large or the structure is complex.

The above is the detailed content of How to remove duplicates from php array. For more information, please follow other related articles on the PHP Chinese website!