How can I use array_map with keys and values, but return an array with the same indexes (not int)?

Question

I have an array such as ['id' => 1, 'name' => 'Fred'].

I want to call array_map on this array and also use the key inside the function. However, when I make a return, my keys will become int.

Simple example :

$arr = array('id' => 1, 'name' => 'Fred');
$result = array_map(
    function ($value, $key) {
        return $value;
     },
     $arr,
     array_keys($arr)
);
var_dump($result);

Basically, I want $result to be identical to $arr in this case, but it turns my string keys into ints.

You need to show what result you want. This works as it should. — AbraCadaver, Aug 26 '14 at 19:15
From the documentation "If the array argument contains string keys then the returned array will contain string keys if and only if exactly one array is passed. _If more than one argument is passed then the returned array always has integer keys_." (emphasis mine) — Patrick Q, Aug 26 '14 at 19:16
`array_map()` is an inappropriate tool for this job. Show us what you actually want to do with this daya. — mickmackusa, Mar 08 '20 at 10:22

Jannie Theunissen · Answer 1 · 2021-07-08T15:07:50.367

24

For your requirement of "I want to call array_map" and "$result to be identical to $arr", try:

$result = array_combine(
     array_keys($arr), 
     array_map(function($v){ return $v; }, $arr)
);

Gives:

   [
     "id" => 1
     "name" => "Fred"
   ]

But heh, if all you want is identical arrays, then nothing beats this code:

$result = $arr;

edited Jul 08 '21 at 15:07

answered Feb 06 '19 at 09:07

Jannie Theunissen

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2

This is not a good generic solution because the transformation function does not have access to the current key. – Walf Mar 24 '22 at 07:25

score 14 · Answer 2 · edited Feb 06 '19 at 08:52

14

The closest you will get using array_map() is this:

<?php
$arr = array('id'=>1,'name'=>'Jon');

$callback = function ($key, $value) {
    return array($key => $value);
  };

$arr = array_map( $callback, array_keys($arr), $arr);
var_dump($arr);
?>

Gives:

   [
     [
       "id" => 1
     ],
     [
       "name" => "Jon"
     ]
   ]

You will be better creating your own function with a foreach inside.

edited Feb 06 '19 at 08:52

Jannie Theunissen

28,256
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answered Aug 26 '14 at 19:17

Marcos

1,240
10
20

The question asks for original keys, not nested arrays with integer keys. – Walf Jun 23 '23 at 06:42

score 4 · Answer 3 · edited Jun 26 '23 at 03:10

What you need is array_walk(). Try this code:

$arr = array('id' => 1, 'name' => 'Fred');
array_walk(
    $arr,
    function (&$value, $key) {
        // do stuff
    }
);
print_r($arr);

Unfortunately, it cannot change the keys but you can change the values if your callback uses them by reference.

If you have to change the keys too, check my other answer regarding reindexing with array_walk().

score 2 · Answer 4 · edited Apr 26 '20 at 06:46

Based on @Jannie Theunissen answer the correct way of getting an array_map working with key for comparing and assigning values based on second array for example is:

$result = array_combine(
 array_keys($arr), 
 array_map(function($v, $key){ return $v; }, $arr, array_keys($arr))
);

Or for optimized alternative:

$keys = array_keys($arr);
$result = array_combine(
 $keys, 
 array_map(function($v, $key){ return $v; }, $arr, $keys)
);

And with a comparison array value:

$compareArray = [/*same structure as $arr but with specific values*/];
$keys = array_keys($arr);
$result = array_combine(
 $keys, 
 array_map(function($v, $key) use ($compareArray) { 
              // recursive can be achieved here passing $v and $compareArray[$key]
              return $compareArray[$key]; 
           }, $arr, $keys)
);

muinh · Answer 5 · 2020-09-25T13:41:38.780

0

The idea is quite simple. You need to use keys inside your array_map() function.

For this purpose we add two arrays: the first one array_keys($array) we pass the keys of our major array and the second one $array is the needed array.

array_map(function($key, $value) {

       // use your key here ...
       return $processed_value;

    }, array_keys($array), $array)

From now on: you can use the $key as a value from first param and $value as a second param.

edited Sep 25 '20 at 13:41

answered Sep 24 '20 at 13:03

muinh

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it would be nice if you can add some explanation words to your solution – mooga Sep 24 '20 at 14:57
2

right you are. thanks for your comment. i've updated my solution with description. – muinh Sep 24 '20 at 20:44
This returns an array with integer keys, which is the problem that is meant to solved. – Walf Mar 24 '22 at 07:27

Walf · Answer 6 · 2023-06-23T07:13:11.627

I don't think I came up with this, but I don't remember where I got it, either.

This function is generic, has the same variadic signature as array_map(), but preserves the keys of the first array passed, and the callback gets the current key as the first arg and the value(s) as the subsequent arg(s), like function ($k, $v, $v2, ..., $vn) {, (whereas array_map() only gets the array values).

function array_map_assoc(callable $callback, array $array, array ...$arrays) {
    $keys = array_keys($array);
    array_unshift($arrays, $keys, $array);
    return array_combine($keys, array_map($callback, ...$arrays));
}

Example: https://3v4l.org/9XQF9

Other examples here have function ($v, $k) { as the callback signature but they're limited to one input array, and it doesn't make sense to have the key in the middle of the values when accepting multiple input arrays.

How can I use array_map with keys and values, but return an array with the same indexes (not int)?

6 Answers6