Can I choose some(not all) elements in an array and shuffle it in PHP?

Question

Can I choose some elements in an array and shuffle it in PHP? You know, when you use

shuffle(array)

, It shuffles all elements in an array, but I just want to shuffle some elements in an array while keep other elements unchanged, how to do it?

Answer 1

You can use array_slice to copy the part of the array you want to shuffle, shuffle the copy, and then use array_splice to copy the shuffled data back into the original array.

EDIT: More generally, if you know the keys of the items you want to shuffle, put them in an array called $keys. Then:

// Get out the items to shuffle.
$work = array();
foreach ($keys as $i => $key) {
    $work[$i] = $myarray[$key];
}

shuffle($work);  // shuffle them

// And put them back.
foreach ($keys as $i => $key) {
    $myarray[$key] = $work[$i];
}

(Sorry if this has some mistakes; my PHP is rusty and I'm not near a computer where I can test it!)

Something very similar will work for a multidimensional array. Each element of $keys could be an array of indices, and instead of $myarray[$key] you would write $myarray[$key[0]][$key[1]].

Answer 2

http://www.php.net/manual/en/function.array-map.php

Answer 3

Consider the following

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

$len = count($a);
for($i = 0; $i < $len; $i++) {
   $j = rand(1, $len) - 1;
   swap($a[$i], $a[$j]);
}

this is the standard loop that shuffles all array elements. To shuffle only some ("movable") elements, let's put their keys into an array

$keys = array(1, 3, 5, 7, 9, 11, 13, 17);

and replace the loop over $a with the loop over $keys

$len = count($keys);
for($i = 0; $i < $len; $i++) {
   $j = rand(1, $len) - 1;
   swap($a[$keys[$i]], $a[$keys[$j]]);
}

this moves elements in positions 1, 3, 5 etc. and leaves other elements in place