How to use array_map with reset callback in php 8 [duplicate]

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 ?

stackoverflow.com/questions/65947307/… maybe that will help — Zurupupz
– Zurupupz, Commented Oct 19, 2021 at 15:30
"Of course, I can use this code instead that but maybe slower than array_map" I think this is false. — AymDev
– AymDev, Commented Oct 19, 2021 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
– IMSoP, Commented Oct 19, 2021 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 minimal reproducible example - some actual example input and code that you can run on its own. — IMSoP
– IMSoP, Commented Oct 20, 2021 at 12:53

IMSoP · Accepted Answer · 2021-10-19 15:31:06Z

5

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.)

answered Oct 19, 2021 at 15:31

IMSoP

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AbraCadaver · Accepted Answer · 2021-10-20 14:10:54Z

1

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');

edited Oct 20, 2021 at 14:10

answered Oct 19, 2021 at 15:32

AbraCadaver

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