How to use array_map with reset callback in php 8

Question

I have a function that work good in php 7 but in php 8.0.11 has warning

$orders->result = array_map('reset', $orders->result);

E_WARNING: reset(): Argument #1 ($array) must be passed by reference, value given in

Of course, I can use this code instead that but maybe slower than array_map

foreach ($orders->result as $item)
       $result[$item[0]['order_id']] = $item[0];

Edit: before foreach or array_map the output like this

    Array
(
    [0] => Array
        (
           [order_id] => 41111909
           [shop_id] => 34277
           [user_id] => 42363
           [status_id] => 4
         )
)

after use foreach output like this

Array
(
    [41111909] => Array
        (
           [order_id] => 41111909
           [shop_id] => 34277
           [user_id] => 42363
           [status_id] => 4
         )
)

How to solve it ?

https://stackoverflow.com/questions/65947307/argument-1-parser-must-be-passed-by-reference maybe that will help — Zurupupz, Oct 19 '21 at 15:30
*"Of course, I can use this code instead that but maybe slower than array_map"* I think this is false. — AymDev, Oct 19 '21 at 15:32
Your alternative code doesn't seem to actually do the same thing - it looks up 'order_id' on each item. It would be equivalent to `array_map(fn($item) => $item[0]['order_id'], $orders->result)`. I also agree with AymDev that it's not particularly likely to be slow. — IMSoP, Oct 19 '21 at 15:36
Your latest edit is **even more** confusing: it's not the result that **either** of the versions of the code you showed would give. I would strongly recommend stepping back and creating a [mre] - some actual example input and code that you can run on its own. — IMSoP, Oct 20 '21 at 12:53
Yes the first line and the other code and arrays don't add up, but edited in a solution for the wanted array. — AbraCadaver, Oct 20 '21 at 14:11

score 4 · Answer 1 · answered Oct 19 '21 at 15:31

The simplest replacement is to make an arrow function (single-expression closure) to get the element for you.

If the arrays are plain lists, so that you're always getting element 0, that's as simple as:

$orders->result = array_map(fn($item) => $item[0], $orders->result);

Another alternative in this case is array_column:

$orders->result = array_colum($orders->result, 0);

If you have other keys, you could use either reset or array_key_first in the callback instead:

$orders->result = array_map(fn($item) => $item[array_key_first($item)], $orders->result);

(I suspect array_key_first will be slightly more efficient, since it doesn't need to manipulate the internal array pointer.)

AbraCadaver · Answer 2 · 2021-10-20T14:10:54.903

It's not entirely clear what you're trying to do, but it seems like you are trying to get the first value from nested arrays. You should be able to use a function:

$orders->result = array_map(function($v) { return reset($v); }, $orders->result);

You may also try using current if it does what you need as it doesn't take a reference and the array pointer should already be reset by array_map:

$orders->result = array_map('current', $orders->result);

After the edit the code in question is not re-indexing the array as you show in the before and after. To do that is simple:

$orders->result = array_column($orders->result, null, 'order_id');

How to use array_map with reset callback in php 8

2 Answers2