Change array key without changing order

Question

You can "change" the key of an array element simply by setting the new key and removing the old:

$array[$newKey] = $array[$oldKey];
unset($array[$oldKey]);

But this will move the key to the end of the array.

Is there some elegant way to change the key without changing the order?

(PS: This question is just out of conceptual interest, not because I need it anywhere.)

Answer 1

Tested and works :)

function replace_key($array, $old_key, $new_key) {
    $keys = array_keys($array);
    if (false === $index = array_search($old_key, $keys, true)) {
        throw new Exception(sprintf('Key "%s" does not exist', $old_key));
    }
    $keys[$index] = $new_key;
    return array_combine($keys, array_values($array));
}

$array = [ 'a' => '1', 'b' => '2', 'c' => '3' ];    
$new_array = replace_key($array, 'b', 'e');

Answer 2

Something like this may also work:

$langs = array("EN" => "English", 
        "ZH" => "Chinese", 
        "DA" => "Danish",
        "NL" => "Dutch", 
        "FI" => "Finnish", 
        "FR" => "French",
        "DE" => "German");
$json = str_replace('"EN":', '"en":', json_encode($langs));
print_r(json_decode($json, true));

OUTPUT:

Array
(
    [en] => English
    [ZH] => Chinese
    [DA] => Danish
    [NL] => Dutch
    [FI] => Finnish
    [FR] => French
    [DE] => German
)

Answer 3

One way would be to simply use a foreach iterating over the array and copying it to a new array, changing the key conditionally while iterating, e.g. if $key === 'foo' then dont use foo but bar:

function array_key_rename($array, $oldKey, $newKey) 
{
    $newArray = [];
    foreach ($array as $key => $value) {
        $newArray[$key === $oldKey ? $newKey : $key] = $value;
    }
    return $newArray;
}

Another way would be to serialize the array, str_replace the serialized key and then unserialize back into an array again. That isnt particular elegant though and likely error prone, especially when you dont only have scalars or multidimensional arrays.

A third way - my favorite - would be you writing array_key_rename in C and proposing it for the PHP core ;)

Answer 4

Check keys existence before proceeding… Otherwise the result can be catastrophic if the new key already exists... or unnecessary processing time/memory consumption if the key to be replaced does not exist.

function array_rename_key( array $array, $old_key, $new_key ) {
    // if $new_key already exists, or if $old_key doesn't exists
    if ( array_key_exists( $new_key, $array ) || ! array_key_exists( $old_key, $array ) ) {
        return $array;
    }

    $new_array = [];
    foreach ( $array as $k => $v ) {
        $new_array[ $k === $old_key ? $new_key : $k ] = $v;
    }

    return $new_array;
}

Answer 5

We are using this function for changing multiple array keys within an array keeping the order:

function replace_keys($array, $keys_map) {
    $keys = array_keys($array);
    foreach($keys_map as $old_key=>$new_key){
        if (false === $index = array_search($old_key, $keys)) {
            continue;
        }
        $keys[$index] = $new_key;
    }
    return array_combine($keys, array_values($array));
}

You can pass an array as $keys_map, like this:

$keys_map=array("old_key_1"=>"new_key_1", "old_key_2"=>"new_key_2",...)

This solution is based on Kristian one.

Answer 6

If possible, one can also put the key to change at the end of the array in the moment of creation :

$array=array('key1'=>'value1','key2'=>'value2','keytochange'=>'value');
$x=$array['keytochange'];
unset($array['keytochange']);
$array['newkey']=$x;

Answer 7

Do a double flip! At least that is all I can think of:

$array=("foo"=>"bar","asdf"=>"fdsa");
$array=array_flip($array);
$array["bar"]=>'newkey';
$array=array_flip($array);

Answer 8

You could use array_combine. It merges an array for keys and another for values...

For instance:

$original_array =('foo'=>'bar','asdf'=>'fdsa');
$new_keys       = array('abc', 'def');
$new_array      = array_combine($new_keys, $original_array);