Switch two items in associative array

Question

Example:

$arr = array(
  \'apple\'      => \'sweet\',
  \'grapefruit\' => \'bitter\',
  \'pear\'       => \'tasty\',
  \'banana\'     => \'yellow\'
)         


        

Answer 1

Here are two solutions. The first is longer, but doesn't create a temporary array, so it saves memory. The second probably runs faster, but uses more memory:

function swap1(array &$a, $key1, $key2)
{
  if (!array_key_exists($key1, $a) || !array_key_exists($key2, $a) || $key1 == $key2) return false;

  $after = array();
  while (list($key, $val) = each($a))
  {
    if ($key1 == $key)
    {
      break;
    }
    else if ($key2 == $key)
    {
      $tmp = $key1;
      $key1 = $key2;
      $key2 = $tmp;
      break;
    }
  }

  $val1 = $a[$key1];
  $val2 = $a[$key2];

  while (list($key, $val) = each($a))
  {
    if ($key == $key2)
      $after[$key1] = $val1;
    else
      $after[$key] = $val;
    unset($a[$key]);
  }

  unset($a[$key1]);
  $a[$key2] = $val2;

  while (list($key, $val) = each($after))
  {
    $a[$key] = $val;
    unset($after[$key]);
  }

  return true;
}

function swap2(array &$a, $key1, $key2)
{    
  if (!array_key_exists($key1, $a) || !array_key_exists($key2, $a) || $key1 == $key2) return false;

  $swapped = array();

  foreach ($a as $key => $val)
  {
    if ($key == $key1)
      $swapped[$key2] = $a[$key2];
    else if ($key == $key2)
      $swapped[$key1] = $a[$key1];
    else
      $swapped[$key] = $val;
  }

  $a = $swapped;

  return true;
}