array_push: my recursive flatten array function seems to reset the final array?

Question

So I'm trying to create a recursive flattenArray function that will take an array (with an unknown number of elements and sub-arrays (with possibly more sub-arrays).

Here's the PHP code I'm having trouble with:

<?php
// Javascript Array [ [1,2,3],[[[4]]],[5],[6],[[7,8,[9]]] ]
// Equivalent PHP Array:   
$sampleArray = Array(
    Array(1,2,3),
    Array(
        Array(
            Array(4)
        )
    ),
    Array(5),
    Array(6),
    Array(
        Array(
            7,
            8,
            Array(9)
        )
    )
);

$finishedArray = Array();

function flattenArray($array){
    foreach ($array as $key => $value) {
        if(is_array($value)){
            flattenArray($value);
        } else {
            $finishedArray[] = $value;
            echo "<br> ".$value." | ";
            print_r($finishedArray);
        }
    }
}

flattenArray($sampleArray);

echo "<br><br>FinishedArray: <br>";
print_r($finishedArray);
?>

I get this output:

1 | Array ( [0] => 1 ) 
2 | Array ( [0] => 1 [1] => 2 ) 
3 | Array ( [0] => 1 [1] => 2 [2] => 3 ) 
4 | Array ( [0] => 4 ) 
5 | Array ( [0] => 5 ) 
6 | Array ( [0] => 6 ) 
7 | Array ( [0] => 7 ) 
8 | Array ( [0] => 7 [1] => 8 ) 
9 | Array ( [0] => 9 ) 

FinishedArray: 
Array ( )

For some reason it resets the $finishedArray. What am I doing wrong here?

Mark Parnell · Accepted Answer · 2013-06-26 03:54:05Z

2

Seems you need to read up on variable scope. There are 2 variables called $finishedArray - one in the main script, and another within the function. Probably the simplest solution would be to pass it via reference:

function flattenArray($array, &$finishedArray){
    foreach ($array as $key => $value) {
        if(is_array($value)){
            flattenArray($value, $finishedArray);
        } else {
            $finishedArray[] = $value;
        }
    }
}

$finishedArray = Array();
flattenArray($sampleArray, $finishedArray);

answered Jun 26, 2013 at 3:54

Mark Parnell

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1 Comment

Boro Over a year ago

Thanks! I even found a simpler fix after seeing your reply: I put "global $finishedArray;" between "function flattenArray($array){" and the foreach statement. Worked like a charm!

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