How to reverse an array in php

In the PHP programming language, array is a commonly used data type. When performing array operations, we sometimes need to reverse the order of elements in the array. We can use PHP built-in functions to achieve this purpose. This article will introduce how to use PHP to reverse an array. The functions involved include array_reverse() and array_flip().

1. array_reverse() function

array_reverse() function is a built-in function in PHP for reversing an array. The syntax is as follows:

array array_reverse (array $array, bool $preserve_keys = false)

Parameter description:

$array: indicates to reverse The reversed array;

$preserve_keys: If the value of this parameter is true, the key names of the original array will be retained in the reversed array. The default is false.

Example demonstration:

$fruits = array(
    "apple",
    "banana",
    "orange",
    "lemon"
);
$reverse_fruits = array_reverse($fruits);
print_r($reverse_fruits);

Output result:

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

2. array_flip() function

array_flip() function is used in PHP Built-in function for exchanging keys and values ​​in an array. If the keys and values ​​in the array are not repeated, you can use this function to easily interchange the keys and values ​​in the array. The operation of reversing an array essentially swaps the index value of the array with its corresponding value. Therefore, using the array_flip() function can also achieve the effect of array reversal.

The syntax of the array_flip() function is as follows:

array array_flip (array $array)

Parameter description:

$array : Indicates the array to be reversed.

Example demonstration:

$fruits = array(
    "apple",
    "banana",
    "orange",
    "lemon"
);
$flip_fruits = array_flip($fruits);
print_r($flip_fruits);

Output result:

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

As mentioned above, when using the array_flip() function to reverse the array, the keys and values ​​of the array will be exchanged. Convenient for array reversal operations. However, we can solve this problem through eccentric techniques. You can first use the array_flip() function to interchange the keys and values ​​of the array, then reverse the array, and then use the array_flip() function to restore the original correspondence between keys and values.

Sample code:

$fruits = array(
    "apple",
    "banana",
    "orange",
    "lemon"
);
$flip_fruits = array_flip($fruits);
$reverse_flip_fruits = array_reverse($flip_fruits, true);
$reverse_fruits = array_flip($reverse_flip_fruits);
print_r($reverse_fruits);

The output result is the same as the array_reverse() function sample code, which is:

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

The above are two methods of reversing an array in PHP: array_reverse () and array_flip() functions. It should be noted that the array reversed using these functions is reversed based on the order of the index values ​​of the original array. If the order of the original array has been disrupted, the reversed result will also be affected.

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