Switch two items in associative array PHP

Question

Example:

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

I want to switch the positions of grapefruit and pear, so the array will become

'apple'=>'sweet','pear'=>'tasty','grapefruit'=>'bitter','banana'=>'yellow')

I know the keys and values of the elements I want to switch, is there an easy way to do this? Or will it require a loop + creating a new array?

Thanks

Answer 1

There is not easy way, just a loop or a new array definition.

And I got a question for you: is this really useful? What convenience do you have in switching them?

Answer 2

Classical associative array doesn't define or guarantee sequence of elements in any way. There is plain array/vector for that. If you use associative array you are assumed to need random access but not sequential. For me you are using assoc array for task it is not made for.

Answer 3

$temp = $array['pear'];
$array['pear'] = $array['grapefruit'];
$array['grapefruit'] = $temp;

Answer 4

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 5

yeah I agree with Lex, if you are using an associative array to hold data, why not using your logic handle how they are accessed instead of depending on how they are arranged in the array.

If you really wanted to make sure they were in a correct order, trying creating fruit objects and then put them in a normal array.

Answer 6

There is no easy way to do this. This sounds like a slight design-logic error on your part which has lead you to try to do this when there is a better way to do whatever it is you are wanting to do. Can you tell us why you want to do this?

You say that I know the keys and values of the elements I want to switch which makes me think that what you really want is a sorting function since you can easily access the proper elements anytime you want as they are.

$value = $array[$key];

If that is the case then I would use sort(), ksort() or one of the many other sorting functions to get the array how you want. You can even use usort() to Sort an array by values using a user-defined comparison function.

Other than that you can use array_replace() if you ever need to swap values or keys.

Answer 7

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 8

This may or may not be an option depending on your particular use-case, but if you initialize your array with null values with the appropriate keys before populating it with data, you can set the values in any order and the original key-order will be maintained. So instead of swapping elements, you can prevent the need to swap them entirely:

$arr = array('apple' => null,
             'pear' => null,
             'grapefruit' => null,
             'banana' => null);

...

$arr['apple'] = 'sweet';
$arr['grapefruit'] = 'bitter'; // set grapefruit before setting pear
$arr['pear'] = 'tasty';
$arr['banana'] = 'yellow';
print_r($arr);

>>> Array
(
    [apple] => sweet
    [pear] => tasty
    [grapefruit] => bitter
    [banana] => yellow
)

Answer 9

Not entirely sure if this was mentioned, but, the reason this is tricky is because it's non-indexed.

Let's take:

$arrOrig = array(
  'fruit'=>'pear',
  'veg'=>'cucumber',
  'tuber'=>'potato'
);

Get the keys:

$arrKeys = array_keys($arrOrig);
print_r($arrKeys);
Array(
 [0]=>fruit
 [1]=>veg
 [2]=>tuber
)

Get the values:

$arrVals = array_values($arrOrig);
print_r($arrVals);
Array(
  [0]=>pear
  [1]=>cucumber
  [2]=>potato
)

Now you've got 2 arrays that are numerical. Swap the indices of the ones you want to swap, then read the other array back in in the order of the modified numerical array. Let's say we want to swap 'fruit' and 'veg':

$arrKeysFlipped = array_flip($arrKeys);
print_r($arrKeysFlipped);
Array (
 [fruit]=>0
 [veg]=>1
 [tuber]=>2
)
$indexFruit = $arrKeysFlipped['fruit'];
$indexVeg = $arrKeysFlipped['veg'];
$arrKeysFlipped['veg'] = $indexFruit;
$arrKeysFlipped['fruit'] = $indexVeg;
print_r($arrKeysFlipped);
Array (
 [fruit]=>1
 [veg]=>0
 [tuber]=>2
)

Now, you can swap back the array:

$arrKeys = array_flip($arrKeysFlipped);
print_r($arrKeys);
Array (
 [0]=>veg
 [1]=>fruit
 [2]=>tuber
)

Now, you can build an array by going through the oringal array in the 'order' of the rearranged keys.

$arrNew = array ();
foreach($arrKeys as $index=>$key) {
  $arrNew[$key] = $arrOrig[$key];
}
print_r($arrNew);
Array (
 [veg]=>cucumber
 [fruit]=>pear
 [tuber]=>potato
)

I haven't tested this - but this is what I'd expect. Does this at least provide any kind of help? Good luck :)

You could put this into a function $arrNew = array_swap_assoc($key1,$key2,$arrOld);

<?php
if(!function_exists('array_swap_assoc')) {
    function array_swap_assoc($key1='',$key2='',$arrOld=array()) {
       $arrNew = array ();
       if(is_array($arrOld) && count($arrOld) > 0) {
           $arrKeys = array_keys($arrOld);
           $arrFlip = array_flip($arrKeys);
           $indexA = $arrFlip[$key1];
           $indexB = $arrFlip[$key2];
           $arrFlip[$key1]=$indexB;
           $arrFlip[$key2]=$indexA;
           $arrKeys = array_flip($arrFlip);
           foreach($arrKeys as $index=>$key) {
             $arrNew[$key] = $arrOld[$key];
           }
       } else {
           $arrNew = $arrOld;
       }
       return $arrNew;
    }
}
?>

WARNING: Please test and debug this before just using it - no testing has been done at all.