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I have an associative array that is many levels deep. I want to convert it to an indexed array (i.e. remove the key names). I don't want to flatten it; I want it to remain a nested array with all of the values intact. What's the best way to accomplish this?

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In PHP, arrays are ordered maps. If your keys are strings, you cannot reliably access elements by numeric offset; you need to actually drop the keys. The simplest way to do that without flattening is to apply array_values() at every level so order is preserved and keys are reindexed from 0 at each depth.

Here is an in-place approach that avoids building a full second copy of the structure, which helps with memory on large trees:

function reindexDeep(&$a) {
    if (!is_array($a)) return;
    foreach ($a as &$v) {
        reindexDeep($v);
    }
    unset($v); // important when using foreach by reference
    $a = array_values($a);
}

Usage:

reindexDeep($data); // $data is modified in place

Notes:

  • Time complexity is O(n). Order is preserved; only the keys are dropped at each level.
  • Mixed numeric keys will be renumbered starting at 0. Scalars and non-arrays are left as-is.
  • Recursion depth depends on your nesting; for extremely deep structures, consider an iterative post-order traversal. Most practical configs handle typical nesting fine.

See the PHP docs for details on array_values, foreach by reference, and how PHP arrays behave.

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Member Avatar for pritaeas

Don't think you have to, you can just access it by index as well.

Member Avatar for broj1

I quickly put together this recursion function.

function assoc2indexedMulti($arr) {

    // initialize destination indexed array
    $indArr = array();

    // loop through source
    foreach($arr as $val) {

        // if the element is array call the recursion
        if(is_array($val)) {

            $indArr[] = assoc2indexedMulti($val);

        // else add the value to destination array
        } else {

            $indArr[] = $val;
        }
    }

    return $indArr;
}

Tested it on a small array, I hope it works OK on your array. If the array is large it might be an issue since it doubles the memory requirement.

Member Avatar for Dani

Thanks, that worked! :)

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