Your algorithm is not a Fisher-Yates shuffle. shuffl chooses a random number between 1 and the number of elements (inclusive) each time. A Fisher-Yates shuffle chooses from a smaller set each iteration to avoid performing a biased shuffle.

Using the dataset A, B, C and D there are 24 possible outcomes (4!), each one with an equal probability of 1/24. The algorithm used for sub shuffl selects 4 random numbers each with a possible value of 1, 2, 3 or 4, or a total of 44 (256) possible outcomes, each with a probability of 1/256 (some of the final permutations are duplicated). 256 is not evenly divisible by 24, so some of the outcomes must be more likely than others.

Update: Oops. BrowserUK's shuffle is indeed a Fisher-Yates shuffle. $a = $_ + rand @{$r} - $_ is parsed as $a = $_ + (rand @{$r} - $_). I assumed it would be parsed as $a = $_ + (rand @{$r}) - $_

In reply to Re: Re: Re: Re: random elements from array - new twist by jsprat
in thread random elements from array - new twist by felwick

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.