recursively build a multi dimensional array of variable depth

Question

I'm parsing a list of URLs from a website and want to build a hierarchical tree of nested arrays.

What I have so far (which works) is below. Because I don't know how deep the levels will go, I'm doing a simple check on the depth and then executing a basic push on to that node.

How can I rewrite this so any number of levels are accommodated?

$tree = array();
$tree[$domain] = array();  // this is the domain root

foreach ( $allMatches as $url ) {

    $foo = parse_url($url );

    // trim "/" from beginning and end
    $bar = trim($foo['path'],'/');
    // for every "/", add a level
    $parts = explode('/', $bar);
    $parts = array_filter($parts, 'strlen');

    // note: there is likely a bug in here.
    // If I process page-1/page-1-1 before page-1,
    // then the leaf or branch containing page-1-1 will be deleted

    if (count($parts) == 1){
        $tree[$domain][$parts[0]] = array();
    }
    if (count($parts) == 2){
        $tree[$domain][$parts[0]][$parts[1]] = array();
    }
    if (count($parts) == 3){
        $tree[$domain][$parts[0]][$parts[1]][$parts[2]] = array();
    }
    if (count($parts) == 4){
        $tree[$domain][$parts[0]][$parts[1]][$parts[2]][$parts[3]] = array();
    }

};

These are the input URLs:

domain.com/page-1
domain.com/page-1/page-1-1
domain.com/page-1/page-1-1/page-1-1-1
domain.com/page-1/page-1-2
domain.com/page-1/page-1-1/page-1-2-1
domain.com/page-2
domain.com/page-2/page-2-1

Note: I do not necessarily need to have domain.com/page-2 in the list in order to generate a leaf for domain.com/page-2/page-2-1

This is the desired resulting structure:

Array
(
    [domain.com] => Array
        (
            [page-1] => Array
                (
                    [page-1-1] => Array
                        (
                            [page-1-1-1] => Array
                                (
                                )
                        )

                    [page-1-2] => Array
                        (
                            [page-1-2-1] => Array
                                (
                                )
                        )
                )

            [page-2] => Array
                (
                    [page-2-1] => Array
                        (
                        )
        )
    )
)

If you don't have page-2 in the list, but you do have page-2/page-2-1 do you want to create the parent node (i.e. page-2), or do you only want page-1-2 as a leaf node? — jake2389
– jake2389, Commented Feb 4, 2017 at 4:13
I would like to create the parent node as well as the leaf in this case. — limeygent
– limeygent, Commented Feb 4, 2017 at 4:19

jake2389 · Accepted Answer · 2017-02-04 04:50:23Z

1

You can do this by using a recursive function if you pass the array as a reference.

$result = array();

function build_array(&$arr, $parts, $i = 0){
    if($i == sizeof($parts))
        return;
    if(!isset($arr[$parts[$i]]))
        $arr[$parts[$i]] = array();
    build_array($arr[$parts[$i]], $parts, $i+1);
}

# Call it like so:
build_array($result, $parts);

Call this function for each url you have and it should work.

Hint: use array_reduce.

Note: If you're doing this in a web context with user input, I would add a depth limit, as you could easily run out of memory with this implementation given a bad input.

answered Feb 4, 2017 at 4:50

jake2389

1,1748 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

limeygent Over a year ago

Excellent. 1 minor modification: $result[$domain] = array(); And it works like a charm.

Collectives™ on Stack Overflow

recursively build a multi dimensional array of variable depth

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related