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Re: Random data generation.

by davies (Parson)
on Jun 26, 2010 at 16:45 UTC ( #846685=note: print w/replies, xml ) Need Help??


in reply to Random data generation.

This is actually a classic algorithm used for things like dealing a pack of cards. If you are dealing bridge hands, for example, you want 52 different cards with no repeats. Some games use multiple packs and/or cut down packs (Bézique uses a pack of 2 decks, A down to 7). You therefore set up a pack with all the possible cards, deal one at random, move the last card to the position from which the card was taken & reduce the pack by one. So, for your problem:
use strict; use warnings; my $nRepeats = 2; my @sSet = qw (a b c d e f); my $nLength = 12; my @sAll; for (1..$nRepeats) { push (@sAll, @sSet); } if ($nLength - 1 > $#sAll) {die "Don't be silly"} my $sString; for (1..$nLength) { my $i = int(rand(@sAll)); $sString .= $sAll[$i]; $sAll[$i] = $sAll[-1]; pop(@sAll); } print "$sString \n";
Now, I'm a beginner. So if anyone sees anything that could be improved (apart from Hungarian notation - it helps me conceptualise strong typing), I'd love to know.

Regards,

John Davies

Update: Re-reading your question, if AABAABAABAAB is valid, my code won't do what you want, but I'm not clear on whether that's what you mean.

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[Corion]: Meh. I have a very simple mechanism to scrape+track prices, and even to send me mail if something changes (via cron), but SQLite doesn't support window functions, so my simple SQL to determine a price change won't work :-( Maybe I should store the DB ...
[Corion]: ... in Pg, but that would mean that I'd have to deal with credentials and stuff :)
[Corion]: In fact, the whole thing is just four simple programs, one App::scrape, another being DBIx::RunSQL, and one some glue to convert a JSON object into an SQL INSERT statement (+DBI connect/execute), so it would be an incredibly simple solution...
[Corion]: ... but that simplicity falls down due to SQLite letting me down and me being too lazy to move to a real DB. Maybe DBD::CSV can handle window functions...
[hippo]: Pg has the "trust" mechanism if you don't fancy using credentials for a trivial db.
[Corion]: hippo: Oooh, that sounds quite nice - let me read the documentation on that :)
[hippo]: https://www. postgresql.org/ docs/current/ static/auth- methods.html#AUTH- TRUST
[erix]: or compile & run an instance as yourself (not user 'postgres')
[erix]: easiest setup is to run with PG* env variables set, and a custom .pgpass files (can be a $PGPASSFILE)

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