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
$arr = array(
'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

Just a little shorter and less complicated than the solution of arcaneerudite:
<?php
if(!function_exists('array_swap_assoc')) {
function array_swap_assoc($key1, $key2, $array) {
$newArray = array ();
foreach ($array as $key => $value) {
if ($key == $key1) {
$newArray[$key2] = $array[$key2];
} elseif ($key == $key2) {
$newArray[$key1] = $array[$key1];
} else {
$newArray[$key] = $value;
}
}
return $newArray;
}
}
$array = $arrOrig = array(
'fruit' => 'pear',
'veg' => 'cucumber',
'tuber' => 'potato',
'meat' => 'ham'
);
$newArray = array_swap_assoc('veg', 'tuber', $array);
var_dump($array, $newArray);
?>
Tested and works fine

Answer 2

Here's my version of the swap function:
function array_swap_assoc(&$array,$k1,$k2) {
if($k1 === $k2) return; // Nothing to do
$keys = array_keys($array);
$p1 = array_search($k1, $keys);
if($p1 === FALSE) return; // Sanity check...keys must exist
$p2 = array_search($k2, $keys);
if($p2 === FALSE) return;
$keys[$p1] = $k2; // Swap the keys
$keys[$p2] = $k1;
$values = array_values($array);
// Swap the values
list($values[$p1],$values[$p2]) = array($values[$p2],$values[$p1]);
$array = array_combine($keys, $values);
}

Answer 3

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 4

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 5

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.

Answer 6

There is no easy way, just a loop or a new array definition.

Answer 7

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 8

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 9

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 10

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;
}

Answer 11

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));
}

Answer 12

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 13

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 14

Well it's just a key sorting problem. We can use uksort for this purpose. It needs a key comparison function and we only need to know that it should return 0 to leave keys position untouched and something other than 0 to move key up or down.
Notice that it will only work if your keys you want to swap are next to each other.
<?php
$arr = array(
'apple' => 'sweet',
'grapefruit' => 'bitter',
'pear' => 'tasty',
'banana' => 'yellow'
);
uksort(
$arr,
function ($k1, $k2) {
if ($k1 == 'grapefruit' && $k2 == 'pear') return 1;
else return 0;
}
);
var_dump($arr);

Answer 15

I'll share my short version too, it works with both numeric and associative arrays.
array array_swap ( array $array , mixed $key1 , mixed $key2 [, bool $preserve_keys = FALSE [, bool $strict = FALSE ]] )
Returns a new array with the two elements swapped. It preserve original keys if specified. Return FALSE if keys are not found.
function array_swap(array $array, $key1, $key2, $preserve_keys = false, $strict = false) {
$keys = array_keys($array);
if(!array_key_exists($key1, $array) || !array_key_exists($key2, $array)) return false;
if(($index1 = array_search($key1, $keys, $strict)) === false) return false;
if(($index2 = array_search($key2, $keys, $strict)) === false) return false;
if(!$preserve_keys) list($keys[$index1], $keys[$index2]) = array($key2, $key1);
list($array[$key1], $array[$key2]) = array($array[$key2], $array[$key1]);
return array_combine($keys, array_values($array));
}
For example:
$arr = array_swap($arr, 'grapefruit', 'pear');

Answer 16

I wrote a function with more general purpose, with this problem in mind.
array with known keys
specify order of keys in a second array ($order array keys indicate key position)
function order_array($array, $order) {
foreach (array_keys($array) as $k => $v) {
$keys[++$k] = $v;
}
for ($i = 1; $i <= count($array); $i++) {
if (isset($order[$i])) {
unset($keys[array_search($order[$i], $keys)]);
}
if ($i === count($array)) {
array_push($keys, $order[$i]);
} else {
array_splice($keys, $i-1, 0, $order[$i]);
}
}
}
foreach ($keys as $key) {
$result[$key] = $array[$key];
}
return $result;
} else {
return false;
}
}
$order = array(1 => 'item3', 2 => 'item5');
$array = array("item1" => 'val1', "item2" => 'val2', "item3" => 'val3', "item4" => 'val4', "item5" => 'val5');
print_r($array); -> Array ( [item1] => val1 [item2] => val2 [item3] => val3 [item4] => val4 [item5] => val5 )
print_r(order_array($array, $order)); -> Array ( [item3] => val3 [item5] => val5 [item1] => val1 [item2] => val2 [item4] => val4 )
I hope this is relevant / helpful for someone

Answer 17

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.