Common array operations in php - array reversal

In PHP, array is a commonly used data structure, which can store a set of related data and provides various convenient operation methods. In actual development, we often need to perform some operations on arrays, such as array sorting, search, interception, etc. This article will introduce a common array operation-array reversal.

Array reversal refers to arranging the elements in the array in the reverse order. Specifically, if the original array is [1,2,3,4,5], then the reversed array is [5,4,3,2,1]. In actual development, array reversal has a wide range of application scenarios. For example, you need to reverse an array when printing a page, or you need to reverse the data of the current page when implementing the paging function.

PHP provides a very convenient array reversal method - array_reverse(). This method can receive an array as a parameter and return a reversed array. Its syntax is very simple, as shown below:

array array_reverse ( array $array [, bool $preserve_keys = FALSE ] )

Among them, the $array parameter is the array to be reversed, and the $preserve_keys parameter indicates whether to retain the key values ​​of the array elements. If this parameter is true, the key name of the element is retained, otherwise the key name will be renumbered. By default, the $preserve_keys parameter is false.

The following is a simple example of using the array_reverse() method to reverse an array:

<?php
    $arr = array(1, 2, 3, 4, 5);
    $reverse_arr = array_reverse($arr);
    print_r($reverse_arr);  // 输出：Array ( [0] => 5 [1] => 4 [2] => 3 [3] => 2 [4] => 1 )
?>

In the above example, we first define an array containing 5 elements and assign it to Variable $arr. Next, we use the array_reverse() method to reverse the array and assign the result to the variable $reverse_arr. Finally, we use the print_r() function to output the reversed array.

It should be noted that using the array_reverse() method to reverse an array does not change the original array, but returns a new reversed array. If you need to change the original array, you can directly assign values ​​to the original array, as shown below:

<?php
    $arr = array(1, 2, 3, 4, 5);
    $arr = array_reverse($arr);
    print_r($arr);  // 输出：Array ( [0] => 5 [1] => 4 [2] => 3 [3] => 2 [4] => 1 )
?>

In actual development, we can not only reverse ordinary arrays, but also reverse associative arrays. The reversal of an associative array is basically the same as the reversal of an ordinary array. You only need to convert the associative array into an ordinary array and then reverse it. The following is an example of reversing an associative array:

<?php
    $arr = array(&#39;name&#39; => '张三', 'age' => 18, 'gender' => '男');
    $reverse_arr = array_reverse($arr, true);
    print_r($reverse_arr);  // 输出：Array ( [gender] => 男 [age] => 18 [name] => 张三 )
?>

In the above example, we first define an associative array containing 3 elements and assign it to the variable $arr. Next, we use the array_reverse() method to reverse the array and set the second parameter to true, which means that the key values ​​of the array elements are retained. Finally, we use the print_r() function to output the reversed array.

In actual development, we can also perform multiple reversal operations on the array for different application scenarios. For example, if you want to reverse the order of an array twice, you can use the following method:

<?php
    $arr = array(1, 2, 3, 4, 5);
    $arr = array_reverse($arr);
    $arr = array_reverse($arr);
    print_r($arr);  // 输出：Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 )
?>

In the above example, we first reverse the array once, and then reverse it the second time. , thereby restoring the array to its original order.

To sum up, array reversal is a common array operation method in PHP, and it is very simple to use. We only need to use the array_reverse() method to quickly reverse an array and implement various application scenarios. In actual development, we can also use multiple methods to perform multiple reversal operations on the array to better meet different needs.

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