The array_reverse() function in PHP is used to reverse the order of the elements in an array. This function does not modify the original array; instead, it returns a new array with the elements in the opposite order.

Syntax:

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

Parameters:

• $array: The input array that you want to reverse.
• $preserve_keys: (Optional) A boolean parameter that determines whether to preserve the original keys. If set to true, the keys will be preserved in the returned array. If set to false (the default), the keys will be re-indexed starting from 0.

Return Value:

• Returns a new array containing the elements of the original array in reverse order.

Example 1: Basic Reversal

In this example, we demonstrate how to use array_reverse() to reverse a simple indexed array.

<?php
$array = [1, 2, 3, 4, 5];
$reversed = array_reverse($array);

print_r($reversed);
?>

Output:

Array
(
    [0] => 5
    [1] => 4
    [2] => 3
    [3] => 2
    [4] => 1
)

In this case, the elements of the original array are reversed, resulting in a new array.

Example 2: Preserving Keys

You can choose to preserve the original keys by setting the second parameter to true.

<?php
$array = ["a" => "apple", "b" => "banana", "c" => "cherry"];
$reversed = array_reverse($array, true);

print_r($reversed);
?>

Output:

Array
(
    [c] => cherry
    [b] => banana
    [a] => apple
)

Here, the keys are preserved, and the resulting array maintains the original key-value associations.

Example 3: Reversing an Empty Array

If you call array_reverse() on an empty array, it will return an empty array.

<?php
$array = [];
$reversed = array_reverse($array);

print_r($reversed);
?>

Output:

Array
(
)

In this case, the output is simply an empty array, as there are no elements to reverse.

Example 4: Reversing Multidimensional Arrays

You can use array_reverse() with multidimensional arrays as well, although it will only reverse the top-level array.

<?php
$array = [
    ["name" => "Alice", "age" => 25],
    ["name" => "Bob", "age" => 30],
    ["name" => "Charlie", "age" => 35],
];
$reversed = array_reverse($array);

print_r($reversed);
?>

Output:

Array
(
    [0] => Array
        (
            [name] => Charlie
            [age] => 35
        )

    [1] => Array
        (
            [name] => Bob
            [age] => 30
        )

    [2] => Array
        (
            [name] => Alice
            [age] => 25
        )
)

Here, the top-level array is reversed, but the inner arrays remain unchanged.

Practical Usage:

• array_reverse() is useful for:
  • Reversing the order of elements in a dataset for processing or display.
  • Implementing functionalities like undo operations where the last item added needs to be processed first.
  • Displaying items in reverse order, such as in a stack or a timeline.

Summary:

• array_reverse($array, $preserve_keys) reverses the order of elements in the specified array and returns a new array.
• You can choose to preserve the original keys or re-index them.
• This function is versatile for various use cases involving array manipulation in PHP, making it a handy tool for developers.