Swap two key/value pairs in an array - php

Question

I have an array:
$array = array('a' => 'val1', 'b' => 'val2', 'c' => 'val3', 'd' => 'val4');
How do I swap any two keys round so the array is in a different order? E.g. to produce this array:
$array = array('d' => 'val4', 'b' => 'val2', 'c' => 'val3', 'a' => 'val1');
Thanks :).

Answer 1

I thought there would be really simple answer by now, so I'll throw mine in the pile:
// Make sure the array pointer is at the beginning (just in case)
reset($array);
// Move the first element to the end, preserving the key
$array[key($array)] = array_shift($array);
// Go to the end
end($array);
// Go back one and get the key/value
$v = prev($array);
$k = key($array);
// Move the key/value to the first position (overwrites the existing index)
$array = array($k => $v) + $array;
This is swapping the first and last elements of the array, preserving keys. I thought you wanted array_flip() originally, so hopefully I've understood correctly.
Demo: http://codepad.org/eTok9WA6

Answer 2

Best A way is to make arrays of the keys and the values. Swap the positions in both arrays, and then put 'em back together.
function swapPos(&$arr, $pos1, $pos2){
$keys = array_keys($arr);
$vals = array_values($arr);
$key1 = array_search($pos1, $keys);
$key2 = array_search($pos2, $keys);
$tmp = $keys[$key1];
$keys[$key1] = $keys[$key2];
$keys[$key2] = $tmp;
$tmp = $vals[$key1];
$vals[$key1] = $vals[$key2];
$vals[$key2] = $tmp;
$arr = array_combine($keys, $vals);
}
Demo: http://ideone.com/7gWKO

Answer 3

Not ideal but does what you want to do:
$array = array('a' => 'val1', 'b' => 'val2', 'c' => 'val3', 'd' => 'val4');
$keys = array_keys($array);
swap($keys, 0, 3);
$values = array_values($array);
swap($values, 0, 3);
print_r(array_combine($keys, $values)); // Array ( [d] => val4 [b] => val2 [c] => val3 [a] => val1 )
function swap (&$arr, $e1, $e2)
{
$temp = $arr[$e1];
$arr[$e1] = $arr[$e2];
$arr[$e2] = $temp;
}
Of course you should also check if both indexes are set in swap function (using isset)

Answer 4

Can't you just store the value to a variable for each?
$val1 = $array[0];
$val2 = $array[3];
$array[0] = $val2;
$array[3] = $val1;

Answer 5

You can use this function to swap any value in array to any key .
/**
* switch value with value on key in given array
* array_switch( array( a, b ,c), c,0 );
* will return array(c, b, a);
*
*
* #param array $array
* #param mixed $value
* #param mixed $key
* #return array
*/
public static function array_switch(&$array, $value, $key)
{
// find the key of current value
$old_key = array_search($value, $array);
// store value on current key in tmep
$tmp = $array[$key];
// set values
$array[$key] = $value;
$array[$old_key] = $tmp;
return $array;
}

Answer 6

I know this is quite old, but I needed this, and couldn't find anything satisfactory. So I rolled my own, and decided to share.
Using just one simple loop, this code is super readable to anyone.
I didn't benchmark, but I have a feeling it's not even that bad compared to the other array_keys, array_values, array_combine versions, even when going through a long array.
Should work for both numerical and string keys alike (only tested with string keys)
It's also easy to implement a check, if one or both keys not found and then throw error or return original array, or whatever you need
function arraySwap(array $array, $key1, $key2) {
$value1 = $array[$key1];
$value2 = $array[$key2];
$newArray = [];
foreach( $array as $key => $value ) {
if ($key === $key1) {
$newArray[$key2] = $value2;
} else if ($key === $key2) {
$newArray[$key1] = $value1;
} else {
$newArray[$key] = $value;
}
}
return $newArray;
}