Detailed explanation of the usage of PHP array_reverse() function

array_reverse() function is a function in PHP used to arrange the elements in an array in reverse order. This function accepts an array as a parameter and returns a new array. The elements in the new array are exactly the same as the elements in the original array, except that their order is reversed.

array_reverse() function has some optional parameters, such as whether to retain the key names of the original array, etc. In this article, we'll take a closer look at how to use the array_reverse() function, its common uses, and how to customize it according to your needs.

Basic usage

array_reverse() function only requires an array as a parameter and returns a new array whose elements are in the opposite order to the original array. The following is a simple example:

$orig_array = array('apple', 'banana', 'cherry', 'date', 'Fig');
$reversed_array = array_reverse($orig_array);

print_r($reversed_array);

The output result is:

Array
(
    [0] => Fig
    [1] => date
    [2] => cherry
    [3] => banana
    [4] => apple
)

As shown above, the order of the elements of the original array has been reversed.

Preserve key names

By default, the array_reverse() function will not retain the key names of the original array, it will regenerate the key names based on the position of the elements in the new array.

If you want to retain the key names of the original array, you can use the optional parameter $preserve_keys. Set it to TRUE, and the array_reverse() function will retain the key names of the original array, as shown below:

$orig_array = array('A'=>'apple', 'B'=>'banana', 'C'=>'cherry', 'D'=>'date', 'E'=>'Fig');
$reversed_array = array_reverse($orig_array, TRUE);

print_r($reversed_array);

The output result is:

Array
(
    [E] => Fig
    [D] => date
    [C] => cherry
    [B] => banana
    [A] => apple
)

As shown above, the $preserver_keys parameter has been set to TRUE, so the elements in the new array have exactly the same key values ​​as the elements in the original array.

Applied to multi-dimensional arrays

The array_reverse() function can also be used for multi-dimensional arrays. In this case, the function will iterate through the array level by level and reverse each sub-array. Here is a simple example:

$orig_array = array(
    'fruits'=>array('apple', 'banana', 'cherry', 'date', 'Fig'),
    'vegetables'=>array('carrot', 'peas', 'potato', 'tomato')
);

$reversed_array = array_reverse($orig_array, TRUE);

print_r($reversed_array);

The output is:

Array
(
    [vegetables] => Array
        (
            [3] => tomato
            [2] => potato
            [1] => peas
            [0] => carrot
        )

    [fruits] => Array
        (
            [4] => Fig
            [3] => date
            [2] => cherry
            [1] => banana
            [0] => apple
        )
)

As shown above, our original array contains a sub-array named fruits and a sub-array named vegetables. In the new array, these subarrays have been reversed and the original key names are preserved.

Custom key names

When using the array_reverse() function, you can also customize the key names of the new array. For example, you can use the optional parameter $new_key to customize the key name of the new array, as follows:

$orig_array = array('apple', 'banana', 'cherry', 'date', 'Fig');
$new_key = 'fruit_reversed';

$reversed_array = array_reverse($orig_array, FALSE);
$reversed_array = array($new_key=>$reversed_array);

print_r($reversed_array);

The output result is:

Array
(
    [fruit_reversed] => Array
        (
            [0] => Fig
            [1] => date
            [2] => cherry
            [3] => banana
            [4] => apple
        )
)

As shown above, the key name of the new array has been is set to fruit_reversed. You can also use the array_reverse() function in combination with the above methods and other custom needs, such as merging multiple arrays into a new reversed array, etc.

Summary

array_reverse() function is a very commonly used function in PHP, used to reverse the elements in an array so that they are arranged in the reverse order. You can use optional parameters to customize the behavior of the function, such as retaining the keys of the original array, setting the keys of the new array, etc. See the PHP documentation for more details.

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