Swap two key/value pairs in an array

Question

I have an array:

$array = array('a' => 'val1', 'b' => 'val2', 'c' => 'val3', 'd' => 'val4');

How do I swap any two keys round so the array is in a different order? E.g. to produce this array:

$array = array('d' => 'val4', 'b' => 'val2', 'c' => 'val3', 'a' => 'val1');

Thanks :).

Answer 1

I thought there would be really simple answer by now, so I'll throw mine in the pile:

// Make sure the array pointer is at the beginning (just in case)
reset($array);

// Move the first element to the end, preserving the key
$array[key($array)] = array_shift($array);

// Go to the end
end($array);

// Go back one and get the key/value
$v = prev($array);
$k = key($array);

// Move the key/value to the first position (overwrites the existing index)
$array = array($k => $v) + $array;

This is swapping the first and last elements of the array, preserving keys. I thought you wanted array_flip() originally, so hopefully I've understood correctly.

Demo: http://codepad.org/eTok9WA6

Answer 2

Best A way is to make arrays of the keys and the values. Swap the positions in both arrays, and then put 'em back together.

function swapPos(&$arr, $pos1, $pos2){
  $keys = array_keys($arr);
  $vals = array_values($arr);
  $key1 = array_search($pos1, $keys);
  $key2 = array_search($pos2, $keys);

  $tmp = $keys[$key1];
  $keys[$key1] = $keys[$key2];
  $keys[$key2] = $tmp;

  $tmp = $vals[$key1];
  $vals[$key1] = $vals[$key2];
  $vals[$key2] = $tmp;

  $arr = array_combine($keys, $vals);
}

Demo: http://ideone.com/7gWKO

Answer 3

Not ideal but does what you want to do:

$array = array('a' => 'val1', 'b' => 'val2', 'c' => 'val3', 'd' => 'val4');

$keys = array_keys($array);
swap($keys, 0, 3);
$values = array_values($array);
swap($values, 0, 3);
print_r(array_combine($keys, $values)); // Array ( [d] => val4 [b] => val2 [c] => val3 [a] => val1 )

function swap (&$arr, $e1, $e2)
{
    $temp = $arr[$e1];
    $arr[$e1] = $arr[$e2];
    $arr[$e2] = $temp;
}

Of course you should also check if both indexes are set in swap function (using isset)