Setting an array item's value as the parent array's key (PHP)

Question

I have an array of array that looks like this:

Array
(
    [0] => Array
        (
            [id] => I100
            [name] => Mary
            [gender] => F
        )
    [1] => Array
        (
            [id] => I101
            [name] => John
            [gender] => M
        )
    [2] => Array
        (
            [id] => I245
            [name] => Sarah
            [gender] => F
        )
)

I want to set the key of the parent array with the value of id, so the result array looks like this:

Array
(
    [I100] => Array
        (
            [id] => I100
            [name] => Mary
            [gender] => F
        )
    [I101] => Array
        (
            [id] => I101
            [name] => John
            [gender] => M
        )
    [I245] => Array
        (
            [id] => I245
            [name] => Sarah
            [gender] => F
        )
)

If possible I'd like to avoid using an additional loop to go through the array and creating a new array to store each item with the proper key, as the array can have thousands of items.

Thanks in advanced!

And what you have tried so far? From where did you were getting this array — Narendrasingh Sisodia, Jan 25 '16 at 12:54
The loop is unavoidable (it can be hidden with a built in function like `array_map` but its still there). Perhaps you can alter the code that generates the array in the 1st place? If not, then loop — Steve, Jan 25 '16 at 12:55
The fastest way is using a loop and not a built in function. — Daan, Jan 25 '16 at 12:57
The code that made the original array is irrelevant as it cannot be altered. — Mike Feng, Jan 25 '16 at 13:00

Steve · Answer 1 · 2016-01-25T13:19:14.010

Despite your caveat, a loop is the obvious solution:

$newArray = [];
foreach($oldArray as $item)
    $newArray[$item['id']] = $item;

If the problem you have is not specifically with a loop, but rather creating a copy of the array is causes excessive memory consumption, then you can edit the array in place, with a for loop:

for($i=0; $i<count($oldArray); $i++){
    $oldArray[$oldArray[$i]['id']] = $oldArray[$i];
    unset($oldArray[$i]);
}

Note this works because the id elements are alphanumeric strings, if they where simple integars then the above code could overwrite sections.

The only other solution is to build the correct array in the 1st place, in a similar manner.

For example, using PDO::fetch instead of PDO::fetchAll:

//$newArray = $sth->fetchAll(PDO::FETCH_ASSOC);
$newArray = [];
while($row = $sth->fetch(PDO::FETCH_ASSOC))
    $newArray[$row['id']] = $row;

OK, well then you have to loop. I just made an edit to give a memory friendly option if thats your actual issue with looping. If thats not, then you need to clarify **why** you dont want to use a loop — Steve, Jan 25 '16 at 13:20

score 1 · Answer 2 · answered Jan 25 '16 at 13:23

1

You can't overwrite keys while iterating through an array "on the fly". So here is solution with array_map which produces an array with needed structure:

// assuming $arr is your initial array
$result = [];

array_map(function($a) use (&$result){
    $result[$a['id']] = $a;
}, $arr);

// $result contains the needed array

answered Jan 25 '16 at 13:23

RomanPerekhrest

88,541
4
65
105

Note this still creates a copy of the array, and is slower than a regular foreach loop, but as the OP has not specified **why** they dont want to use a loop, this is technically a reasonable answer – Steve Jan 25 '16 at 13:25
I also wish to know how someone is going to change all keys in initial array on the fly without loop and creating new array – RomanPerekhrest Jan 25 '16 at 13:32

score 0 · Answer 3 · answered Jan 25 '16 at 12:58

0

You can add needed key during creation of this array.

answered Jan 25 '16 at 12:58

Saleniex

615
5
4

Well that's a pretty stupid answer as it has already been said in the comments. – Daan Jan 25 '16 at 13:01

Setting an array item's value as the parent array's key (PHP)

3 Answers3