Move an array element to a new index in PHP

As commented, 2x array_splice, there even is no need to renumber:

$array = [
    0 => 'a', 
    1 => 'c', 
    2 => 'd', 
    3 => 'b', 
    4 => 'e',
];

function moveElement(&$array, $a, $b) {
    $out = array_splice($array, $a, 1);
    array_splice($array, $b, 0, $out);
}

moveElement($array, 3, 1);

Result:

[
    0 => 'a',
    1 => 'b',
    2 => 'c',
    3 => 'd',
    4 => 'e',
];

The solution from hakre with two array_splice commands doesn't work with named arrays. The key of the moved element will be lost.

Instead you can splice the array two times and merge the parts.

function moveElement(&$array, $a, $b) {
    $p1 = array_splice($array, $a, 1);
    $p2 = array_splice($array, 0, $b);
    $array = array_merge($p2,$p1,$array);
}

How does it work:

• First: remove/splice the element from the array
• Second: splice the array into two parts at the position you want to insert the element
• Merge the three parts together

Example:

$fruits = array(
    'bananas'=>'12', 
    'apples'=>'23',
    'tomatoes'=>'21', 
    'nuts'=>'22',
    'foo'=>'a',
    'bar'=>'b'
);

moveElement($fruits, 1, 3);

// Result
['bananas'=>'12', 'tomatoes'=>'21', 'nuts'=>'22', 'apples'=>'23', 'foo'=>'a', 'bar'=>'b']

A lot of good answers. Here's a simple one built on the answer by @RubbelDeCatc. The beauty of it is that you only need to know the array key, not its current position (before repositioning).

/**
 * Reposition an array element by its key.
 *
 * @param array      $array The array being reordered.
 * @param string|int $key They key of the element you want to reposition.
 * @param int        $order The position in the array you want to move the element to. (0 is first)
 *
 * @throws \Exception
 */
function repositionArrayElement(array &$array, $key, int $order): void
{
    if(($a = array_search($key, array_keys($array))) === false){
        throw new \Exception("The {$key} cannot be found in the given array.");
    }
    $p1 = array_splice($array, $a, 1);
    $p2 = array_splice($array, 0, $order);
    $array = array_merge($p2, $p1, $array);
}

Straight forward to use:

$fruits = [
    'bananas'=>'12', 
    'apples'=>'23',
    'tomatoes'=>'21', 
    'nuts'=>'22',
    'foo'=>'a',
    'bar'=>'b'
];

repositionArrayElement($fruits, "foo", 1);

var_export($fruits);

/** Returns
array (
  'bananas' => '12',
  'foo' => 'a', <--  Now moved to position #1
  'apples' => '23',
  'tomatoes' => '21',
  'nuts' => '22',
  'bar' => 'b',
)
**/

Works on numeric arrays also:

$colours = ["green", "blue", "red"];

repositionArrayElement($colours, 2, 0);

var_export($colours);

/** Returns
array (
  0 => 'red', <-- Now moved to position #0
  1 => 'green',
  2 => 'blue',
)
*/

Demo

Arrays in PHP are not actual array in the C sens but associative arrays. But the way to move a value from an index to another is quiet straight forward and is the same as in C++:

Copy the value to move to a temporary buffer, translate all the elements to crush the empty spot at the source position and in the same free up a spot on the destination position. Put the backup value in the destination spot.

function moveElement ($a , $i , $j)
{
      $tmp =  $a[$i];
      if ($i > $j)
      {
           for ($k = $i; $k > $j; $k--) {
                $a[$k] = $a[$k-1]; 
           }        
      }
      else
      { 
           for ($k = $i; $k < $j; $k++) {
                $a[$k] = $a[$k+1];
           }
      }
      $a[$j] = $tmp;
      return $a;
}


$a = array(0, 1, 2, 3, 4, 5);
print_r($a);

$a = moveElement($a, 1, 4);
echo ('1 ->  4');
print_r($a);


$a = moveElement($a, 5, 0);
echo ('5 ->  0' );
print_r($a);

Output:

Array
(
    [0] => 0
    [1] => 1
    [2] => 2
    [3] => 3
    [4] => 4
    [5] => 5
)
1 ->  4Array
(
    [0] => 0
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 1
    [5] => 5
)
5 ->  0Array
(
    [0] => 5
    [1] => 0
    [2] => 2
    [3] => 3
    [4] => 4
    [5] => 1
)

You'll need to add some Exception handling to have a complete code.