How to rename the key in a foreach loop? - php

Question

I'm trying to generate an XML from a database call, and the utility class I'm using throws an error Illegal character in tag name. tag: 0
I figured this is because of the array being [0],[1],[2] etc. Really I should set them all to be something standard, like 'asset' since they are all assets, but I can't do that because then keys will be identical, but maybe the ID would work. But I don't know how to change the key that I'm on within a foreach loop.
I tried:
foreach ($assets as &$key => &$asset) {
$key2 = $asset->isci;
$asset = get_object_vars($asset);
}
But I cannot pass reference for $key.
This is a brief representation of what the array looks like:
array(2) {
[0]=>
array(25) {
["id"]=>
string(2) "27"
}
[1]=>
array(25) {
["id"]=>
string(2) "25"
}
[2]=>
array(25) {
["id"]=>
string(1) "1"
}
}

Answer 1

Modifying keys of an array while looping over it is generally a bad idea - even if the language supported it, it can be very confusing to debug.
The simplest approach is to simply build a new array based on the old one, but with better keys:
$rekeyed_assets = array();
foreach ($assets as $old_key => $asset)
{
$new_key = $asset->isci;
$asset = get_object_vars($asset);
$rekeyed_assets[ $new_key ] = $asset;
}

Answer 2

The most convenient way is to change all the keys and then use array_combine to create a new array with the modified keys. Here's how you can do that in bulk using array_map and an anonymous function:
$newKeys = array_map(function($asset) { return $asset->isci; }, $assets);
$assets = array_combine($newKeys, $assets);
You can also do the same for the values:
$newKeys = array_map(function($asset) { return $asset->isci; }, $assets);
$newValues = array_map(function($asset) { return get_object_vars($asset); }, $assets);
$assets = array_combine($newKeys, $newValues);
This method does have a drawback (increased memory usage) which may be an issue if your array has millions of items, but in that case it's highly likely that it would be better to restructure the program so that it does not need to keep huge arrays in memory in the first place.