Function to flatten a multidimensional array doesn't work as expected - php

Question

All I am trying to do is flatten an arbitrary array of integers.
Here is my code:
<?php
$list_of_lists_of_lists = [[1, 2, [3]], [4, 3, 4, [5, 3, 4]], 3];
$flattened_list = [];
function flatten($l){
foreach ($l as $value) {
if (is_array($value)) {
flatten($value);
}else{
$flattened_list[] = $value;
}
}
}
flatten($list_of_lists_of_lists);
print_r($flattened_list);
?>
When I run this code, I get this:
Array ( )
I have no idea why. I did the exact same code in Python and it worked fine.
Can you guys point out, where I went wrong?

Answer 1

First you have a scope issue, that your result array is out of scope in the function. So just pass it as argument from call to call.
Second you also don't return your result array, which you have to do, if you want to use the result outside of the function.
Corrected code:
$list_of_lists_of_lists = [[1, 2, [3]], [4, 3, 4, [5, 3, 4]], 3];
function flatten($l, $flattened_list = []){
foreach ($l as $value) {
if(is_array($value)) {
$flattened_list = flatten($value, $flattened_list);
} else {
$flattened_list[] = $value;
}
}
return $flattened_list;
}
$flattened_list = flatten($list_of_lists_of_lists);
print_r($flattened_list);
output:
Array
(
[0] => 1
[1] => 2
[2] => 3
[3] => 4
[4] => 3
[5] => 4
[6] => 5
[7] => 3
[8] => 4
[9] => 3
)