How to remove duplicates from php array

As a popular programming language, PHP provides convenient and efficient array operation methods, in which removing duplicate elements is a common requirement. This article will introduce several methods to implement PHP array deduplication and analyze their advantages and disadvantages in depth.

1. Use the array_unique function

The easiest way is to use PHP's built-in function array_unique(). This function will return a new array after deduplication, and it will not change the original array. The following is a sample code:

$array = array('apple', 'banana', 'orange', 'banana', 'pear');
$new_array = array_unique($array);
print_r($new_array);

The output result is:

Array
(
    [0] => apple
    [1] => banana
    [2] => orange
    [4] => pear
)

array_unique() function uses a hash table algorithm, which is highly efficient, but if the array element types are inconsistent, the result will be Unpredictable. Additionally, this function cannot handle keys for associative arrays, only numeric arrays, so in some cases other approaches need to be considered.

2. Use loops and in_array function

The second method is to use loops and in_array() function to manually remove duplicates. The in_array() function can check whether a value already exists in the array. The following is the sample code:

$array = array('apple', 'banana', 'orange', 'banana', 'pear');
$new_array = array();
foreach ($array as $value) {
    if (!in_array($value, $new_array)) {
        $new_array[] = $value;
    }
}
print_r($new_array);

The output result is the same as the first method. This method has better flexibility than the array_unique() function and can handle the keys of associative arrays, but it requires manual writing of loop code, which is relatively troublesome and may be less efficient if there are many array elements.

3. Use the array_flip and array_keys functions

The third method is to use the array_flip() and array_keys() functions, which are used to exchange the keys and values ​​of the array respectively, and return all keys of the array of a new array. The purpose of using these two functions is to convert the original array into a numeric array, and then use the array_unique() function. The following is sample code:

$array = array('apple', 'banana', 'orange', 'banana', 'pear');
$new_array = array_unique(array_keys(array_flip($array)));
print_r($new_array);

The output results are the same as the first two methods. This method is more concise than the second method and does not change the original array, but it requires two additional operations, which may have an adverse impact on performance.

4. Use recursion and array_merge function

The last method is to use recursion and array_merge() function to deduplicate multi-dimensional arrays. This method can handle arrays of arbitrary dimensions. The following is a sample code:

$array = array('apple', 'banana', array('orange', 'banana'), 'pear');
$new_array = array();
function array_recursive_unique($array) {
    global $new_array;
    foreach ($array as $value) {
        if (is_array($value)) {
            array_recursive_unique($value);
        } else {
            if (!in_array($value, $new_array)) {
                $new_array[] = $value;
            }
        }
    }
}
array_recursive_unique($array);
print_r($new_array);

The output result is:

Array
(
    [0] => apple
    [1] => banana
    [2] => orange
    [3] => pear
)

The advantage of this method is that it can handle arrays of arbitrary dimensions and does not require additional functions. But it requires manual writing of recursive code, which is relatively cumbersome and inefficient. For large arrays, the running time can be very long.

To sum up, this article introduces four common methods to achieve PHP array deduplication. Using the array_unique() function is the simplest and easiest to understand, but it cannot handle keys of associative arrays. You can handle any array type using loops and the in_array() function, but you need to write the loop code manually. Working with keys of associative arrays works well using the array_flip() and array_keys() functions, but requires additional operations. Arrays of arbitrary dimensions can be processed using recursion and the array_merge() function, but manually writing recursive code or using large-scale arrays may cause efficiency problems. The appropriate method should be selected based on actual needs and specific scenarios.

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