PHP Change Array Keys

Question

If you have an array of keys that you want to use then use array_combine

Given $keys = array('a', 'b', 'c', ...) and your array, $list, then do this:

$list = array_combine($keys, array_values($list));

List will now be array('a' => 'blabla 1', ...) etc.

You have to use array_values to extract just the values from the array and not the old, numeric, keys.

That's nice and simple looking but array_values makes an entire copy of the array so you could have space issues. All we're doing here is letting php do the looping for us, not eliminate the loop. I'd be tempted to do something more like:

foreach ($list as $k => $v) {
   unset ($list[$k]);

   $new_key =  *some logic here*

   $list[$new_key] = $v;
}

I don't think it's all that more efficient than the first code but it provides more control and won't have issues with the length of the arrays.

No, there is not, for starters, it is impossible to have an array with elements sharing the same key

$x =array(); 
$x['foo'] = 'bar' ; 
$x['foo'] = 'baz' ; #replaces 'bar'

Secondarily, if you wish to merely prefix the numbers so that

$x[0] --> $x['foo_0']  

That is computationally implausible to do without looping. No php functions presently exist for the task of "key-prefixing", and the closest thing is "extract" which will prefix numeric keys prior to making them variables.

The very simplest way is this:

function rekey( $input , $prefix ) { 
    $out = array(); 
    foreach( $input as $i => $v ) { 
        if ( is_numeric( $i ) ) { 
            $out[$prefix . $i] = $v; 
            continue; 
        }
        $out[$i] = $v;
    }
    return $out;
}

Additionally, upon reading XMLWriter usage, I believe you would be writing XML in a bad way.

<section> 
    <foo_0></foo_0>
   <foo_1></foo_1>
   <bar></bar>
   <foo_2></foo_2>
</section>

Is not good XML.

<section> 
   <foo></foo>
   <foo></foo>
   <bar></bar>
   <foo></foo>
</section>

Is better XML, because when intrepreted, the names being duplicate don't matter because they're all offset numerically like so:

section => { 
    0 => [ foo , {} ]
    1 => [ foo , {} ]
    2 => [ bar , {} ]
    3 => [ foo , {} ] 
}

I added this for an answer to another question and seemed relevant. Hopefully might help someone that needs to change the value of the keys in an array. Uses built-in functions for php.

$inputArray = array('app_test' => 'test', 'app_two' => 'two');

/**
 * Used to remap keys of an array by removing the prefix passed in
 * 
 * Example:
 * $inputArray = array('app_test' => 'test', 'app_two' => 'two');
 * $keys = array_keys($inputArray);
 * array_walk($keys, 'removePrefix', 'app_');
 * $remappedArray = array_combine($keys, $inputArray);
 *
 * @param $value - key value to replace, should be from array_keys
 * @param $omit - unused, needed for prefix call
 * @param $prefix - prefix to string replace in keys
 */
function removePrefix(&$value, $omit, $prefix) {
    $value = str_replace($prefix, '', $value);
}

// first get all the keys to remap
$keys = array_keys($inputArray);

// perform internal iteration with prefix passed into walk function for dynamic replace of key
array_walk($keys, 'removePrefix', 'app_');

// combine the rewritten keys and overwrite the originals
$remappedArray = array_combine($keys, $inputArray);

// see full output of comparison
var_dump($inputArray);
var_dump($remappedArray);

Output:

array(2) {
  'attr_test' =>
  string(4) "test"
  'attr_two' =>
  string(3) "two"
}
array(2) {
  'test' =>
  string(4) "test"
  'two' =>
  string(3) "two"
}

$prefix = '_';
$arr = array_combine(
    array_map(function($v) use ($prefix){
       return $prefix.$v;
    }, array_keys($arr)),
    array_values($arr)
);

I think that he want:

$a = array(1=>'first_name', 2=>'last_name');
$a = array_flip($a);

$a['first_name'] = 3;
$a = array_flip($a);

print_r($a);

The solution to when you're using XMLWriter (native to PHP 5.2.x<) is using $xml->startElement('itemName'); this will replace the arrays key.