Question

I am attempting a basic recursion to create multi-dimensional arrays based on the values of an inputed array.

The recursion works by checking for a value we shall call it “recursion” to start the loop and looks for another value we’ll call it “stop_recursion” to end.

Basically taking this array

array('One', 'Two', 'recursion', 'Three', 'Four', 'Five', 'stop_recursion', 'Six', 'Seven')

And making this array

array('One', 'Two', array('Three', 'Four', 'Five'), 'Six', 'Seven')

The code I have for it so far is as follows

function testRecrusion($array, $child = false)
{
    $return = array();

    foreach ($array as $key => $value) {
        if ($value == 'recursion') {
            unset($array[$key]);
            $new = testRecrusion($array, true);
            $array = $new['array'];
            $return[] = $new['return'];
        } else {
            if ($value == 'stop_recursion') {
                unset($array[$key]);
                if ($child) {
                    return array('return' => $return, 'array' => $array);
                }
            } else {
                unset($array[$key]);
                $return[] = $value;
            }
        }
    }

    return $return;
}

But the output from that is

Array
(
    [0] => One
    [1] => Two
    [2] => Array
        (
            [0] => Three
            [1] => Four
            [2] => Five
        )

    [3] => Three
    [4] => Four
    [5] => Five
    [6] => Six
    [7] => Seven
)

I guess the real question is…will an array values continuously loop through the first values given from the initial call or once the new array is returned and set will it loop through that new array. I know the answer is basically right here saying that yes it will continue the old array value, but shouldn’t this work vice-versa?

Any help will be appreciated 🙂

———— edit ——————-

I might as well add that while I can perform this action using a much simpler method, this needs to be recursively checked since this will be ported to a string parser that could have a infinite number of child arrays.

Answer 1

When you return inside the recursion, you need to return both the inner array and the index from which to continue searching for elements so that you don’t look at the same element twice. Try this instead:

function testRecursionImpl($array, $i)
{
    $return = array();

    for (; $i < sizeof($array); ++$i) {
        if ($array[$i] == 'recursion') {
            $new = testRecursionImpl($array, $i + 1);
            $return[] = $new[0];
            $i = $new[1];
        } else if ($array[$i] == 'stop_recursion') {
            return array($return, $i);
        } else {
            $return[] = $array[$i];
        }
    }

    return array($return, $i);
}

function testRecursion($array)
{
    $result = testRecursionImpl($array, 0);
    return $result[0];
}