Swap array values with php

Question

I have an array:

array(
    0 => 'contact',
    1 => 'home',
    2 => 'projects'
);

and I need to swap the 'contact' with 'home', so the array would be like:

array(
    0 => 'home',
    1 => 'contact',
    2 => 'projects'
);

how can I do this with PHP? :)

Answer 1

I wrote simple function array_swap: swap two elements between positions swap_a & swap_b.

function array_swap(&$array,$swap_a,$swap_b){
   list($array[$swap_a],$array[$swap_b]) = array($array[$swap_b],$array[$swap_a]);
}

For OP question (for example):

$items = array(
  0 => 'contact',
  1 => 'home',
  2 => 'projects'
);

array_swap($items,0,1);
var_dump($items);
// OUTPUT

array(3) {
   [0]=> string(4) "home"
   [1]=> string(7) "contact"
   [2]=> string(8) "projects"
 }

Update Since PHP 7.1 it's possible to do it like:

$items = [
  0 => 'contact',
  1 => 'home',
  2 => 'projects'
];

[$items[0], $items[1]] = [$items[1], $items[0]];

var_dump($items);
// OUTPUT

array(3) {
   [0]=> string(4) "home"
   [1]=> string(7) "contact"
   [2]=> string(8) "projects"
 }

It's possible through Symmetric array destructuring.

Answer 2

Try this:

$a = array(
    0 => 'contact',
    1 => 'home',
    2 => 'projects'
);
$temp = $a[0];
$a[0] = $a[1];
$a[1] = $temp;

Answer 3

In PHP 7.1+ syntax, you can use this

[$Array[$a], $Array[$b]] = [$Array[$b], $Array[$a]];

Answer 4

Just use a temp variable to hold one value as you swap the other. Then restore the first with the temp variable. For numbers there are other methods that don't require the use of temp variables but here it's the best (only?) way.

$a = array(
    0 => 'contact',
    1 => 'home',
    2 => 'projects'
);

print_r($a);
Array ( [0] => contact [1] => home [2] => projects )

$tmp = $a[0];
$a[0] = $a[1];
$a[1] = $tmp;

print_r($a);
Array ( [0] => home [1] => contact [2] => projects )

Answer 5

New answer: (as others have expressed)

I was not aware of Symmetric Array Destructuring at the time of posting, but that is a functionless, one-liner swapping technique -- I'd use that all day long.

A relevant blog post/tutorial. An example implemention for bubble sorting.

Code: (Demo)

$a = ['contact', 'home', 'projects'];

[$a[0], $a[1]] = [$a[1], $a[0]];

var_export($a);

---

Old answer:

If you want to avoid using temporary data storage, or love a one-liner use array_replace().

array_replace() will make adjustments in accordance with the indices:

Code: (Demo)

$a = array(
    0 => 'contact',
    1 => 'home',
    2 => 'projects'
);

var_export(array_replace($a,[$a[1],$a[0]]));

Output:

array (
  0 => 'home',
  1 => 'contact',
  2 => 'projects',
)

Answer 6

Just use a temp variable to hold it. So:

$temp = $array[0];
$array[0] = $array[1];
$array[1] = $temp;

That way you don't lose the value of one of them.

Answer 7

I tested the 4 ways proposed to compare the performance:

$array=range(0,9999); //First 10000 natural numbers
$time=-microtime(true); //Start time
for($i=0;$i<1000000;++$i){ //1 Millon swaps
    $a=array_rand($array); //Random position: ~60ms
    $b=array_rand($array); //Random position: ~60ms
    //Using a temp variable: ~70ms
    $temp=$array[$a];$array[$a]=$array[$b];$array[$b]=$temp;
    //Using list language construct: ~ 140ms
    list($array[$a],$array[$b])=array($array[$b],$array[$a]);
    //Using PHP 7.1+ syntax: ~ 140ms
    [$array[$a],$array[$b]]=[$array[$b],$array[$a]];
    //Using array_replace function: ~ 28000ms
    array_replace($array,[$array[$a],$array[$b]]);
}
$time+=microtime(true); //Elapsed time
echo "Time: ",sprintf('%f', $time)," seconds";

Although it is probably not the most comfortable way, using a temporary variable seems to be 2x faster than the next 2 methods, and 400x faster than using the array_replace function.

Answer 8

$array = array(
    0 => 'home',
    1 => 'contact',
    2 => 'projects'
);

$t = $array[0];
$array[0] = $array[1];
$array[1] = $t;

would be a simple enough approach…

Answer 9

$x = array('a', 'b', 'c', 'd');
array_splice($x, 1, 2, array_reverse(array_slice($x, 1, 2)));
var_dump($x);

array_splice can replace a reversed array_slice

Answer 10

Solution:

$a = array(
    0 => 'contact',
    1 => 'home',
    2 => 'projects'
);

list($a[0], $a[1]) = [$a[1], $a[0]];

I have made function for it

function swap(&$a, &$b){
    list($a, $b) = [$b, $a];
}

Usage:

swap($a[0], $a[1]);