Moving array element to top in PHP

$arr = array(
    'a1'=>'1',
    'a2'=>'2'
);

I need to move the a2 to the top, as well as keep the a2开发者_开发百科 as a key how would I go on about it I can't seem to think a way without messing something up :)

Here is a solution which works correctly both with numeric and string keys:

function move_to_top(&$array, $key) {
    $temp = array($key => $array[$key]);
    unset($array[$key]);
    $array = $temp + $array;
}

It works because arrays in PHP are ordered maps.
Btw, to move an item to bottom use:

function move_to_bottom(&$array, $key) {
    $value = $array[$key];
    unset($array[$key]);
    $array[$key] = $value;
}

You can achieve that this way:

$arr = array(
    'a1'=>'1',
    'a2'=>'2'
);

end($arr);

$last_key     = key($arr);
$last_value   = array_pop($arr);
$arr          = array_merge(array($last_key => $last_value), $arr);

/*
    print_r($arr);

    will output (this is tested):
    Array ( [a2] => 2 [a1] => 1 )
*/

try this:

$key = 'a3';
$arr = [
    'a1' => '1',
    'a2' => '2',
    'a3' => '3',
    'a4' => '4',
    'a5' => '5',
    'a6' => '6'
];
if (isset($arr[ $key ]))
    $arr = [ $key => $arr[ $key ] ] + $arr;

result:

array(
    'a3' => '3',
    'a1' => '1',
    'a2' => '2',
    'a4' => '4',
    'a5' => '5',
    'a6' => '6'
)

Here's a simple one liner to get this done with array_splice() and the union operator:

$arr = array('a1'=>'1', 'a2'=>'2', 'a3' => '3');
$arr = array_splice($arr,array_search('a2',array_keys($arr)),1) + $arr;

Edit:

In retrospect I'm not sure why I wouldn't just do this:

$arr = array('a2' => $arr['a2']) + $arr;

Cleaner, easier and probably faster.

You can also look at array_multisort This lets you use one array to sort another. This could, for example, allow you to externalize a hard-coded ordering of values into a config file.

<?php
   $ar1 = array(10, 100, 100, 0);
   $ar2 = array(1, 3, 2, 4);
   array_multisort($ar1, $ar2);

   var_dump($ar1);
   var_dump($ar2);
?>

In this example, after sorting, the first array will contain 0, 10, 100, 100. The second array will contain 4, 1, 2, 3. The entries in the second array corresponding to the identical entries in the first array (100 and 100) were sorted as well.

Outputs:

array(4) {
  [0]=> int(0)
  [1]=> int(10)
  [2]=> int(100)
  [3]=> int(100)
}
array(4) {
  [0]=> int(4)
  [1]=> int(1)
  [2]=> int(2)
  [3]=> int(3)
}