PHP : flatten array - fastest way?

Question

Is there any fast way to flatten an array and select subkeys ('key'&'value' in this case) without running a foreach loop, or is the foreach always the fastest way?

Array
(
    [0] => Array
        (
            [key] => string
            [value] => a simple string
            [cas] => 0
        )

    [1] => Array
        (
            [key] => int
            [value] => 99
            [cas] => 0
        )

    [2] => Array
        (
            [key] => array
            [value] => Array
                (
                    [0] => 11
                    [1] => 12
                )

            [cas] => 0
        )

)

To:

Array
(
    [int] => 99
    [string] => a simple string
    [array] => Array
        (
            [0] => 11
            [1] => 12
        )
)

Duplicate: http://stackoverflow.com/questions/1319903/how-to-flatten-a-multidimensional-array I think this answer will help you the most: http://stackoverflow.com/questions/1319903/how-to-flatten-a-multidimensional-array/1320156#1320156 — Felix Kling, May 28 '10 at 16:46

score 3 · Accepted Answer · answered May 28 '10 at 16:50

3

Give this a shot:

$ret = array();
while ($el = each($array)) {
    $ret[$el['value']['key']] = $el['value']['value'];
}

answered May 28 '10 at 16:50

ircmaxell

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oh what an ancient operators :) – Your Common Sense May 28 '10 at 17:01
I would recomend always initializing the array iterator using `reset($array)` just before iterating that way, to avoid that another call to, e.g. `end()` would have messed with it. Lots of ways to fall for that trap... – Gui Prá Feb 18 '13 at 17:29

score 3 · Answer 2 · edited Dec 10 '13 at 10:56

3

call_user_func_array("array_merge", $subarrays) can be used to "flatten" nested arrays.
What you want is something entirely different. You could use array_walk() with a callback instead to extract the data into the desired format. But no, the foreach loop is still faster. There's no array_* method to achieve your structure otherwise.

edited Dec 10 '13 at 10:56

VisioN

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answered May 28 '10 at 16:52

mario

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array_walk wouldn't work in itself, because it doesn't return anything except a bool (and you can't modify the key of the array). – ircmaxell May 28 '10 at 17:04

score 0 · Answer 3 · answered Sep 27 '18 at 02:13

Hopefully it will help someone else, but here is a function I use to flatten arrays and make nested elements more accessible.

Usage and description here: https://totaldev.com/flatten-multidimensional-arrays-php/

The function:

// Flatten an array of data with full-path string keys
function flat($array, $separator = '|', $prefix = '', $flattenNumericKeys = false) {
    $result = [];

    foreach($array as $key => $value) {
        $new_key = $prefix . (empty($prefix) ? '' : $separator) . $key;

        // Make sure value isn't empty
        if(is_array($value)) {
            if(empty($value)) $value = null;
            else if(count($value) == 1 && isset($value[0]) && is_string($value[0]) && empty(trim($value[0]))) $value = null;
        }

        $hasStringKeys = is_array($value) && count(array_filter(array_keys($value), 'is_string')) > 0;
        if(is_array($value) && ($hasStringKeys || $flattenNumericKeys)) $result = array_merge($result, flat($value, $separator, $new_key, $flattenNumericKeys));
        else $result[$new_key] = $value;
    }

    return $result;
}

Zenexer · Answer 4 · 2013-08-13T00:28:30.683

This should properly combine arrays with integer keys. If the keys are contiguous and start at zero, they will be dropped. If an integer key doesn't yet exist in the flat array, it will be kept as-is; this should mostly preserve non-contiguous arrays.

function array_flatten(/* ... */)
{
    $flat = array();
    array_walk_recursive(func_get_args(), function($value, $key)
    {
        if (array_key_exists($key, $flat))
        {
            if (is_int($key))
            {
                $flat[] = $value;
            }
        }
        else
        {
            $flat[$key] = $value;
        }
    });
    return $flat;
}

You could use !isset($key) or empty($key) instead to favor useful values.

Here's a more concise version:

function array_flatten(/* ... */)
{
    $flat = array();
    array_walk_recursive(func_get_args(), function($value, $key) use (&$flat)
    {
        $flat = array_merge($flat, array($key => $value));
    });
    return $flat;
}

PHP : flatten array - fastest way?

4 Answers4

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