Beefy Boxes and Bandwidth Generously Provided by pair Networks
There's more than one way to do things
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

Howdy all,

I have a function that I use sometimes when I need permutations (I do permutation-testing often for stats problems). Currently I require the user to pass the "cardinality": how many different elements to put in each class. Let me give a simple example first, before I show the code:

Data: a1, b2, c3 Cardinality: 1 Permutations: {a1, b2}, {a1, c3}, {b2, c3}, Data: a1, b2, c3, d4 Cardinality: 2 Permutations: {{a1, b2}, {c3, d4}} {{a1, c3}, {b2, d4}} {{a1, d4}, {c3, d4}}

I hope that's reasonably clear: cardinality defines the size of the group I wish to obtain permutations of. The first example above was: all possible pairs of groups of one element. The second example was: all possible pairs of groups of three elements (triplets). Within a single permutation, no element can be repeated, and I take only unique permutations.

I am generating all these permutations into a data-structure for later use (e.g. passing them to other software, writing them to file with their results, sending them to a DB, etc.). The code that does this is pretty simple, but unfortunately it has required me to HARDCODE the cardinality. It looks like this:

my @data; if ($cardinality == 1) { for (my $i = 0; $i < scalar(@$permlist); $i++) { for (my $j = 0; $j < scalar(@$permlist); $j++) { push @data, { first => [$$permlist[$i]], second => [$$permlist[$j]], }; } } } if ($cardinality == 2) { for (my $i = 0; $i < scalar(@$permlist); $i++) { for (my $j = 0; $j < scalar(@$permlist); $j++) { for (my $k = 0; $k < scalar(@$permlist); $k++) { for (my $p = 0; $p < scalar(@$permlist); $p++) { push @data, { first => [$$permlist[$i], $$permlist[$j]], second => [$$permlist[$k], $$permlist[$p]], }; } } } } }

And so on for higher cardinality. I would prefer to have a generalized way of doing this, rather than needing a separate set of for-loops for each cardinality. Is that possible? I'm turned it over in my head, and haven't found a way yet.


In reply to Generalizing Code: Generating Unique Permutations by Anonymous Monk

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!
  • 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, 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, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • Outside of code tags, you may need to use entities for some characters:
            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.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others cooling their heels in the Monastery: (11)
    As of 2014-12-18 08:40 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      Is guessing a good strategy for surviving in the IT business?





      Results (47 votes), past polls