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tamewhale
tamewhale

Reputation: 1061

How do I move an array element with a known key to the end of an array in PHP?

Having a brain freeze over a fairly trivial problem. If I start with an array like this:

$my_array = array(
                  'monkey'  => array(...),
                  'giraffe' => array(...),
                  'lion'    => array(...)
);

...and new elements might get added with different keys but always an array value. Now I can be sure the first element is always going to have the key 'monkey' but I can't be sure of any of the other keys.

When I've finished filling the array I want to move the known element 'monkey' to the end of the array without disturbing the order of the other elements. What is the most efficient way to do this?

Every way I can think of seems a bit clunky and I feel like I'm missing something obvious.

Upvotes: 66

Views: 70807

Answers (4)

You Old Fool
You Old Fool

Reputation: 22941

I really like @Gordon's answer for its elegance as a one liner, but it only works if the targeted key exists in the first element of the array. Here's another one-liner that will work for a key in any position:

$arr = ['monkey' => 1, 'giraffe' => 2, 'lion' => 3];
$arr += array_splice($arr, array_search('giraffe', array_keys($arr)), 1);

Demo

  • Beware, this fails with numeric keys because of the way that the array union operator (+=) works with numeric keys (Demo).
  • Also, this snippet assumes that the targeted key is guaranteed to exist in the array. If the targeted key does not exist, then the result will incorrectly move the first element to the end because array_search() will return false which will be coalesced to 0 by array_splice() (Demo).

Upvotes: 4

Andrea
Andrea

Reputation: 107

You can implement some basic calculus and get a universal function for moving array element from one position to the other.

For PHP it looks like this:

function magicFunction ($targetArray, $indexFrom, $indexTo) { 
    $targetElement = $targetArray[$indexFrom]; 
    $magicIncrement = ($indexTo - $indexFrom) / abs ($indexTo - $indexFrom); 

    for ($Element = $indexFrom; $Element != $indexTo; $Element += $magicIncrement){ 
        $targetArray[$Element] = $targetArray[$Element + $magicIncrement]; 
    } 

    $targetArray[$indexTo] = $targetElement; 
}

Check out "moving array elements" at "gloommatter" for detailed explanation.

http://www.gloommatter.com/DDesign/programming/moving-any-array-elements-universal-function.html

Upvotes: -1

Gordon
Gordon

Reputation: 316969

array_shift is probably less efficient than unsetting the index, but it works:

$my_array = array('monkey' => 1, 'giraffe' => 2, 'lion' => 3);
$my_array['monkey'] = array_shift($my_array);
print_r($my_array);

Another alternative is with a callback and uksort:

uksort($my_array, create_function('$x,$y','return ($y === "monkey") ? -1 : 1;'));

You will want to use a proper lambda if you are using PHP5.3+ or just define the function as a global function regularly.

Upvotes: 13

cletus
cletus

Reputation: 625037

The only way I can think to do this is to remove it then add it:

$v = $my_array['monkey'];
unset($my_array['monkey']);
$my_array['monkey'] = $v;

Upvotes: 129

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