Switch two items in associative array

Question

Example:

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


        

Answer 1

Arrays in php are ordered maps.

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

doesn't mean that that the first element is 'apple'=>'sweet' and the last - 'banana'=>'yellow' just because you put 'apple' first and 'banana' last. Actually, 'apple'=>'sweet' will be the first and 'banana'=>'yellow' will be the second because of alphabetical ascending sort order.

Answer 2

if the array comes from the db, add a sort_order field so you can always be sure in what order the elements are in the array.

Answer 3

function arr_swap_keys(array &$arr, $key1, $key2, $f_swap_vals=false) {
   // if f_swap_vals is false, then
   // swap only the keys, keeping the original values in their original place
   // ( i.e. do not preserve the key value correspondence )
   // i.e. if arr is (originally)
   // [ 'dog' => 'alpha', 'cat' => 'beta', 'horse' => 'gamma' ]
   // then calling this on arr with, e.g. key1 = 'cat', and key2 = 'horse'
   // will result in arr becoming: 
   // [ 'dog' => 'alpha', 'horse' => 'beta', 'cat' => 'gamma' ]
   // 
   // if f_swap_vals is true, then preserve the key value correspondence
   // i.e. in the above example, arr will become:
   // [ 'dog' => 'alpha', 'horse' => 'gamma', 'cat' => 'beta' ]
   // 
   // 

   $arr_vals = array_values($arr); // is a (numerical) index to value mapping
   $arr_keys = array_keys($arr);   // is a (numerical) index to key mapping
   $arr_key2idx = array_flip($arr_keys);
   $idx1 = $arr_key2idx[$key1];
   $idx2 = $arr_key2idx[$key2];
   swap($arr_keys[$idx1], $arr_keys[$idx2]);
   if ( $f_swap_vals ) {
      swap($arr_vals[$idx1], $arr_vals[$idx2]);
   }
   $arr = array_combine($arr_keys, $arr_vals);
}

function swap(&$a, &$b) {
   $t = $a;
   $a = $b;
   $b = $t;
}

Answer 4

There is an easy way:

$sourceArray = array(
    'apple'      => 'sweet',
    'grapefruit' => 'bitter',
    'pear'       => 'tasty',
    'banana'     => 'yellow'
);
// set new order
$orderArray = array(
    'apple'      => '', //this values would be replaced
    'pear'       => '',
    'grapefruit' => '',
    //it is not necessary to touch all elemets that will remains the same
);
$result = array_replace($orderArray, $sourceArray);
print_r($result);

and you get:

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

Answer 5

fwiw here is a function to swap two adjacent items to implement moveUp() or moveDown() in an associative array without foreach()

/**
 * @param array  $array     to modify
 * @param string $key       key to move
 * @param int    $direction +1 for down | -1 for up
 * @return $array
 */
protected function moveInArray($array, $key, $direction = 1)
{
    if (empty($array)) {
        return $array;
    }
    $keys  = array_keys($array);
    $index = array_search($key, $keys);
    if ($index === false) {
        return $array; // not found
    } 
    if ($direction < 0) {
        $index--;
    }
    if ($index < 0 || $index >= count($array) - 1) {
        return $array; // at the edge: cannot move
    } 

    $a          = $keys[$index];
    $b          = $keys[$index + 1];
    $result     = array_slice($array, 0, $index, true);
    $result[$b] = $array[$b];
    $result[$a] = $array[$a];
    return array_merge($result, array_slice($array, $index + 2, null, true)); 
}