Switch two items in associative array

Question

Example:

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


        

Answer 1

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;
}