How to Flatten Array in PHP

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Sheeraz Gul Feb 02, 2024
PHP PHP Array
  1. Use the Recursiveiteratoriterator and Recursivearrayiterator to Operate Flatenning the Array in PHP
  2. Use the array_walk_recursive to Flatten a Multidimensional Array in PHP
  3. Use the for Loop to Flatten a Multidimensional Array in PHP
  4. Use the while Loop to Flatten a Multidimensional Array in PHP
  5. Use the foreach Loop to Flatten a Multidimensional Array in PHP
How to Flatten Array in PHP

Flatten array means converting a multidimensional array into a one-dimensional array. PHP has different ways to flatten an array, and we will discuss them here.

Use the Recursiveiteratoriterator and Recursivearrayiterator to Operate Flatenning the Array in PHP

The SPL library has iterators that are used to flatten the multidimensional arrays. We used two iterators, RecursiveIteratorIterator and RecursiveArrayIterator, to operate flattening the array.

<?php
$demo_array = array('a', 'b', 'c', 'd', array('e', 'f', 'g', 'h',  array('i', 'j', 'k'), 'l', 'm', 'n', 'o'), 'p', 'q', 'r', 's');
$iter_object = new RecursiveIteratorIterator(new RecursiveArrayIterator($demo_array));
$flatten_array= array();
foreach($iter_object as $value) {
  array_push($flatten_array,$value);
}
print_r($flatten_array);
?>

Output:

Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f [6] => g [7] => h [8] => i [9] => j [10] => k [11] => l [12] => m [13] => n [14] => o [15] => p [16] => q [17] => r [18] => s )

The code contains a three-layer array that will be flattened in a one-dimensional array.

Use the array_walk_recursive to Flatten a Multidimensional Array in PHP

The built-in function array_walk_recursive can be used with a closure function to flatten a multidimensional array in PHP.

<?php
function flatten_array(array $demo_array) {
    $new_array = array();
    array_walk_recursive($demo_array, function($array) use (&$new_array) { $new_array[] = $array; });
    return $new_array;
}
$demo_array = array('a', 'b', 'c', 'd', array('e', 'f', 'g', 'h',  array('i', 'j', 'k'), 'l', 'm', 'n', 'o'), 'p', 'q', 'r', 's');

$new_array = flatten_array($demo_array);

print_r($new_array);
?>

Output:

Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f [6] => g [7] => h [8] => i [9] => j [10] => k [11] => l [12] => m [13] => n [14] => o [15] => p [16] => q [17] => r [18] => s )

The array_walk_recursive with a closure function flattens the given multidimensional array.

Use the for Loop to Flatten a Multidimensional Array in PHP

We can use for loops to flatten multidimensional arrays; additional built-in functions may be required.

<?php
function flatten_array($demo_array,$new_array) {
    for($i = 0; $i < count($demo_array); $i++) {
        if(is_array($demo_array[$i])) {
            $new_array = flatten_array($demo_array[$i], $new_array);
        }
        else {
            if(isset($demo_array[$i])) {
            $new_array[] = $demo_array[$i];
            }
        }
    }
    return $new_array;
}

$demo_array = array('a', 'b', 'c', 'd', array('e', 'f', 'g', 'h',  array('i', 'j', 'k'), 'l', 'm', 'n', 'o'), 'p', 'q', 'r', 's');
print_r(flatten_array($demo_array, array()));
?>

Output:

Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f [6] => g [7] => h [8] => i [9] => j [10] => k [11] => l [12] => m [13] => n [14] => o [15] => p [16] => q [17] => r [18] => s )

The above code will generate a flattened array by iterating the given array with the help of the for loop.

Use the while Loop to Flatten a Multidimensional Array in PHP

<?php
function flatten_array ($demo_array){
    $x = 0;
    while ($x < count ($demo_array)){
        while (is_array ($demo_array[$x])){
            if (!$demo_array[$x]){
                array_splice ($demo_array, $x, 1);
                --$x;
                break;
            }
            else{
                array_splice ($demo_array, $x, 1, $demo_array[$x]);
            }
        }
        ++$x;
    }
    return $demo_array;
}
$demo_array = array('a', 'b', 'c', 'd', array('e', 'f', 'g', 'h',  array('i', 'j', 'k'), 'l', 'm', 'n', 'o'), 'p', 'q', 'r', 's');
print_r(flatten_array($demo_array));
?>

Output:

Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f [6] => g [7] => h [8] => i [9] => j [10] => k [11] => l [12] => m [13] => n [14] => o [15] => p [16] => q [17] => r [18] => s )

The given array flattens with the help of the while loop and array_splice function, which is used to remove a part of an array and replace it with something else.

Use the foreach Loop to Flatten a Multidimensional Array in PHP

<?php
function flatten_array($demo_array) {
    if (!is_array($demo_array)) {
        // make sure the input is an array
        return array($demo_array);
    }

    $new_array = array();
    foreach ($demo_array as $value) {
        $new_array = array_merge($new_array, flatten_array($value));
    }

    return $new_array;
}

$demo_array = array('a', 'b', 'c', 'd', array('e', 'f', 'g', 'h',  array('i', 'j', 'k'), 'l', 'm', 'n', 'o'), 'p', 'q', 'r', 's');
print_r(flatten_array($demo_array));
?>

Output:

Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f [6] => g [7] => h [8] => i [9] => j [10] => k [11] => l [12] => m [13] => n [14] => o [15] => p [16] => q [17] => r [18] => s )

The given array flattens using the foreach loop and array_merge() function, which combines two arrays into one.

Author: Sheeraz Gul
Sheeraz Gul avatar Sheeraz Gul avatar

Sheeraz is a Doctorate fellow in Computer Science at Northwestern Polytechnical University, Xian, China. He has 7 years of Software Development experience in AI, Web, Database, and Desktop technologies. He writes tutorials in Java, PHP, Python, GoLang, R, etc., to help beginners learn the field of Computer Science.

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