in reply to random number generation.

A particularly simple approach is: 

use List::Util qw( shuffle );
my @picks = (shuffle 1..15)[0..4];

[download]

For picking a few numbers from a very long list, "rerolling" duplicates is probably the most efficient: 

my @picks;
my %seen;
for (1..5) {                          # Five numbers
   my $pick = int(rand(15000)) + 1;   # in 1..15000.
   redo if $seen{$pick}++;
   push @picks, $pick;
}

[download]
Update: Added second method.

Replies are listed 'Best First'.
Re^2: random number generation.
by newbio (Beadle) on Sep 11, 2007 at 18:15 UTC 
    Thanks guys for your replies.

Hi Ikegami, how would your "rerolling duplicates" method work if the l
+ist just thrice (not long enough) the total numbers to be drawn. I gu
+ess "shuffle" would be a better alternative then?

Thanks.

    [download]
[reply]
[d/l]
      The shorter the list, the more rerolls would have to be done. shuffle will work quite well in most settings even with hundreds of items.
[reply]
[d/l]
        Thank you very much Ikegami.

One last thing, if I want to create 3 sets of 5 integers each from the
+ integer range 1 to 15 then which one is better from randomness angle
+:

1. I shuffle the previously "shuffled" list in each iteration, or
2. I shuffle the "original" list in each iteration.

Here is the code:

Method 1:
my @array=(1..15);
my @shufflednumbers=();

foreach my $i (1..3) {
    @shufflednumbers = shuffle (@array);
    print "@shufflednumbers[0..4]";
    @shufflednumbers=();
}

Method 2:
my @array=(1..15);
my @temp=@array;
my @shufflednumbers=();

foreach my $i (1..3) {
    @shufflednumbers = shuffle (@temp);
    print "@shufflednumbers[0..4]";
    @temp=@shufflednumbers;
    @shufflednumbers=();
}

        [download]
[reply]
[d/l]

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