PHP Exercises: Deep flatten an given array

Last update on May 27 2025 13:09:16 (UTC/GMT +8 hours)

79. Deep Array Flattening

Write a PHP program to deep flatten an given array.

Sample Solution:

PHP Code:

<?php
// Function definition for 'deep_flatten' that takes an array of items as a parameter
function deep_flatten($items)
{
    // Initialize an empty array to store the flattened result
    $result = [];

    // Iterate through each item in the array
    foreach ($items as $item) {
        // Check if the current item is not an array
        if (!is_array($item)) {
            // If not an array, add the item to the result array
            $result[] = $item;
        } else {
            // If the current item is an array, recursively call 'deep_flatten' on the item and merge the result with the current result array
            $result = array_merge($result, deep_flatten($item));
        }
    }

    // Return the flattened result array
    return $result;
}

// Call 'deep_flatten' with a nested array as a parameter and assign the result to the variable '$result'
$result = deep_flatten([1, [2], [[3], 4], 5, 6]); 

// Display the result using 'print_r'
print_r($result);
?>

Explanation:

Define deep_flatten Function:

The deep_flatten function takes an array, potentially containing nested arrays, and returns a single, flat array with all elements.

Initialize an Empty Array:

An empty array $result is created to store the flattened elements.

Iterate Through Each Item in the Array:

Uses a foreach loop to iterate over each item in $items.

Check if an Item is Not an Array:

If an item is not an array, it is appended to $result directly.

Recursively Flatten Nested Arrays:

If an item is an array, deep_flatten calls itself recursively on that item.
Uses array_merge to add the flattened result of this nested array to $result.

Return Flattened Array:

Once all items are processed, the fully flattened array $result is returned.

Call deep_flatten and Display Result:

deep_flatten is called with [1, [2], [[3], 4], 5, 6], resulting in [1, 2, 3, 4, 5, 6].
print_r outputs the final flattened array to the screen.

Output:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
)

Flowchart:

For more Practice: Solve these Related Problems:

Write a PHP script to recursively flatten a multidimensional array into a single-level array without using built-in functions.
Write a PHP script to traverse a nested array structure and output a flat array of all values.
Write a PHP function to perform a deep flatten operation on an array containing nested arrays of arbitrary depth.
Write a PHP script to iterate through an array recursively and collect all elements into a flat list.

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PHP Code Editor:

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