How to use random () function to shuffle array in PHP

Question

In one interview I was asked to shuffle an associative array that has value like .

$card = array (
               "car"=>1,
                "bus"=>2,
                "truck"=>3,
);

etc. Using a radom function that generate random digit between 0,1 ;

They asked me not to use any inbuilt PHP function .

input: associative array;
output: randomly sequenced associative array;

Thanks & Regards

@b0s3 :) Yes I have tried doing something , I will update my code though its not working yet — Vikram Anand Bhushan, Jul 02 '15 at 04:27
"They asked me not to use any inbuilt PHP function" so write php with out php - that would be a great skill — , Jul 02 '15 at 04:32
and um if your going to put code in your profile, how about making valid? — , Jul 02 '15 at 04:35
Fetch the keys using `array_keys()`, then use Fisher-Yates shuffle on that, then rebuild the array. — Ja͢ck, Jul 02 '15 at 05:23
@Dagon Actually, `shuffle()` wouldn't work out of the box, because it will lose the associative keys ;-) — Ja͢ck, Jul 02 '15 at 05:25
My implementation with mt_rand better than shuffle() http://stackoverflow.com/a/43532529/960020 — Stalingrad, Apr 21 '17 at 01:47

Ja͢ck · Accepted Answer · 2015-07-02T05:40:40.430

2

The built-in shuffle() doesn't handle associative arrays very well, so you'd need to shuffle the array keys and then reconstitute the array again.

I'm using the Fisher-Yates-Knuth algorithm to perform the shuffling, which is really the crux of the solution.

function myshuffle($arr)
{
    // extract the array keys
    $keys = [];
    foreach ($arr as $key => $value) {
        $keys[] = $key;
    }

    // shuffle the keys    
    for ($i = count($keys) - 1; $i >= 1; --$i) {
        $r = mt_rand(0, $i);
        if ($r != $i) {
            $tmp = $keys[$i];
            $keys[$i] = $keys[$r];
            $keys[$r] = $tmp;
        }
    }

    // reconstitute
    $result = [];
    foreach ($keys as $key) {
        $result[$key] = $arr[$key];
    }

    return $result;
}

edited Jul 02 '15 at 05:40

answered Jul 02 '15 at 05:37

Ja͢ck

170,779
38
263
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we can not use any array built in function – NullPoiиteя Jul 02 '15 at 05:38
@NullPoiиteя Actually, OP said "They asked me not to use *any* inbuilt PHP function" .. that would include `rand()` though lol – Ja͢ck Jul 02 '15 at 05:39
so true ... so -1 :D for using foreach, count, and mt_rand LOL – NullPoiиteя Jul 02 '15 at 05:54
Good thing `foreach` is not a built-in function ;-) – Ja͢ck Jul 02 '15 at 05:56
ohh my bad .. its loop, And your shuffling logic is better than mine i just created mess, didnt thought abuot that – NullPoiиteя Jul 02 '15 at 05:57
thought it can be easily done by shuffling key from keys array shuffle($keys); – NullPoiиteя Jul 02 '15 at 06:07
@NullPoiиteя Yeah, the whole midsection can disappear with a simple `shuffle()` call =S – Ja͢ck Jul 02 '15 at 06:37

score -2 · Answer 2 · answered Jul 02 '15 at 05:59

-2

    $words = array("adumbrate","antipathy","aspersion","assiduous","cacophony","conundrum");


 $rand_word_index = array_rand($words); // Get any random index from an array

        //  Original Word
 $rand_word = $words[$rand_word_index]; // Stored array value basis of random index


$shuffled = str_shuffle($rand_word); // Shuffle this value or word

echo $shuffled;

answered Jul 02 '15 at 05:59

Mahesh Shukla

186
10

you can not use built in array function .. read the question carefully please – NullPoiиteя Jul 02 '15 at 06:01
Also, this gives a string and not an array. – Ja͢ck Jul 02 '15 at 06:02

How to use random () function to shuffle array in PHP

2 Answers2