How to get elements in reverse order of an array in PHP ?

An array is a collection of elements stored together. Every element in an array belong to a similar data type. The elements in the array are recognized by their index values. The elements can be subjected to a variety of operations, including reversal.

There are various ways to reverse the elements of an array : 

Using for Loop

Using for Loop, a decrement for loop can be initiated in order to access the elements in the reverse order. The index begins at the length of the array - 1 until it reaches the beginning of the array. During each iteration, the inbuilt array_push method is called, which is used to push the elements to the newly declared array maintained for storing reverse contents. 

Syntax:

array_push($array, $element)

<?php
    // Declaring an array
    $arr = array(1, 2, 3, 4, 5);
    echo("Original Array : ");
    print_r($arr);

    // Declaring an array to store reverse
    $arr_rev = array();
    for($i = sizeof($arr) - 1; $i >= 0; $i--) {
        array_push($arr_rev,$arr[$i]);
    }

    echo("Modified Array : ");
    print_r($arr_rev);
?>

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

Using array_reverse() Method

the array_reverse() function can be used to reverse the contents of the specified array. The output is also returned in the form of an array.

Syntax:

array_reverse($array)

<?php
    // Declaring an array
    $arr = array(1, 2, 3, 4, 5);
    echo("Original Array : ");
    print_r($arr);

    // Reversing array
    $arr_rev = array_reverse($arr);
    echo("Modified Array : ");
    print_r($arr_rev);
?>

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

Using the array_reduce Function

The array_reduce function can reverse an array by iteratively prepending each element to a new array. This method processes the original array and constructs a reversed version by adding each item to the front of the new array.

Example:

<?php

$array = [1, 2, 3, 4, 5];
$reversedArray = array_reduce($array, function($carry, $item) {
    array_unshift($carry, $item);
    return $carry;
}, []);
print_r($reversedArray);

?>

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

Using array_walk()

In PHP, array_walk() iterates through an array and applies a callback function to each element. To reverse an array using array_walk(), prepend each element to a new array using array_unshift() within the callback function.

Example

<?php
$array = [1, 2, 3, 4, 5];
$reversedArray = [];

array_walk($array, function($item) use (&$reversedArray) {
    array_unshift($reversedArray, $item);
});

print_r($reversedArray); // Output: Array ( [0] => 5 [1] => 4 [2] => 3 [3] => 2 [4] => 1 )
?>

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

Using Stack (array_push and array_pop)

This method involves using the stack data structure, where elements are pushed onto the stack and then popped off in the reverse order.

Example: In this example, the reverseArray function initializes an empty stack and an empty array to hold the reversed elements. It then iterates through the input array, pushing each element onto the stack. After all elements are on the stack, the function repeatedly pops elements from the stack and appends them to the reversed array.

<?php
  function reverseArray($array) {
    $stack = [];
    $reversedArray = [];

    // Push all elements onto the stack
    foreach ($array as $element) {
        array_push($stack, $element);
    }

    // Pop all elements from the stack to form the reversed array
    while (!empty($stack)) {
        $reversedArray[] = array_pop($stack);
    }

    return $reversedArray;
}


$arr = [1, 2, 3, 4, 5];
$reversedArr = reverseArray($arr);
print_r($reversedArr);

?>

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

Using the array_reduce Function

The array_reduce function can reverse an array by iteratively prepending each element to a new array. This method processes the original array and constructs a reversed version by adding each item to the front of the new array.

Example:

<?php
function reverseArrayUsingReduce($array) {
    return array_reduce($array, function($carry, $item) {
        array_unshift($carry, $item);
        return $carry;
    }, []);
}


$array = ['G', 'e', 'e', 'k', 's'];
$reversed_array = reverseArrayUsingReduce($array);
print_r($reversed_array);

?>

Array
(
    [0] => s
    [1] => k
    [2] => e
    [3] => e
    [4] => G
)