Array functions in PHP8: various usage techniques of array_reverse()

When writing PHP code, arrays are one of the most commonly used data structures by developers. In order to process array data more efficiently, PHP8 provides many practical array functions, including the array_reverse() function. This article will introduce various usage techniques of array_reverse() function to help developers better apply this function in daily work.

1. Basic introduction to the array_reverse() function

The array_reverse() function is used to reverse the order of the elements of an array and return the result as a new array after the flipping. The syntax format is as follows:

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

Parameter description:

• $array: required parameter, the original array variable or initial value array to be flipped.
• $preserve_keys: Optional parameter, specifies whether to retain the corresponding relationship between key names and key values ​​in the original array. The default value is FALSE, which is not retained.

Note: The array_reverse() function does not change the contents of the original array, but returns a new flipped array. Developers should pay attention when using it.

2. Tips for using the array_reverse() function

1. Reverse the order of array elements

The most common usage scenario is to reverse the order of an array element Inversion can be achieved through the following sample code:

$arr = array('a', 'b', 'c', 'd', 'e'); 
$rev_arr = array_reverse($arr); 
print_r($rev_arr);

After executing the above code, the output result is:

Array
(
    [0] => e
    [1] => d
    [2] => c
    [3] => b
    [4] => a
)

2. Keep the key name of the original array

If you need to retain the corresponding relationship between key names and key values ​​in the original array, you can set the $preserve_keys parameter to TRUE. The sample code is as follows:

$arr = array('name'=>'Tom', 'age'=>20, 'gender'=>'male'); 
$rev_arr = array_reverse($arr, TRUE); 
print_r($rev_arr);

After executing the above code, the output result is:

Array
(
    [gender] => male
    [age] => 20
    [name] => Tom
)

3. Reverse only a part of the elements of the array

Sometimes you only need to reverse the array Partial elements are flipped, rather than the entire array. This can be achieved by using the array_slice() function. The sample code is as follows:

$arr = array('a', 'b', 'c', 'd', 'e'); 
$rev_arr = array_slice($arr, 0, 3); //取前三个元素
$rev_arr = array_reverse($rev_arr); 
$arr = array_merge($rev_arr, array_slice($arr, 3)); //合并前三个元素和后两个元素
print_r($arr);

After executing the above code, the output result is:

Array
(
    [0] => c
    [1] => b
    [2] => a
    [3] => d
    [4] => e
)

4. Used in multi-dimensional arrays

array_reverse() function can handle any type of array, including multi-dimensional arrays. The sample code is as follows:

$arr = array(
    array('id'=>1, 'name'=>'Jack', 'age'=>20),
    array('id'=>2, 'name'=>'Rose', 'age'=>22),
    array('id'=>3, 'name'=>'Tom', 'age'=>18),
); 
foreach ($arr as &$row) {
    $row = array_reverse($row, TRUE);
}
print_r($arr);

The output result after executing the above code is:

Array
(
    [0] => Array
        (
            [age] => 20
            [name] => Jack
            [id] => 1
        )

    [1] => Array
        (
            [age] => 22
            [name] => Rose
            [id] => 2
        )

    [2] => Array
        (
            [age] => 18
            [name] => Tom
            [id] => 3
        )

)

The above code first traverses the entire two-dimensional array, and then performs the array_reverse() operation on each sub-array, thereby realizing the entire two-dimensional array. Element-wise reversal of a dimensional array.

5. Used together with the array_keys() function

The array_reverse() function is usually used together with the array_keys() function to obtain the key list of the array returned by other functions and Turn it over. The sample code is as follows:

$arr = array('name'=>'Tom', 'age'=>20, 'gender'=>'male'); 
$key_arr = array_keys($arr);
$rev_key_arr = array_reverse($key_arr);
print_r($rev_key_arr);

The output result after executing the above code is:

Array
(
    [0] => gender
    [1] => age
    [2] => name
)

The above code uses the array_keys() function to obtain the key list of the array, then flips it and outputs it.

3. Summary

The array_reverse() function is one of the practical array functions in PHP8. It can reverse an array very conveniently. During the development process, combining a variety of techniques can maximize the role of the array_reverse() function and improve development efficiency. I hope the techniques introduced in this article can be helpful to the majority of PHP developers.

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