Keep It Simple, Stupid PerlMonks

### Re: Non-Repetitive Random Numbers

by BrowserUk (Pope)
 on Apr 05, 2013 at 13:10 UTC ( #1027135=note: print w/replies, xml ) Need Help??

in reply to Non-Repetitive Random Numbers

The problem with most of the solutions offered is that they create a list the size of the range of numbers required (100,000) in order to obtain the sample of 30 values. Many compound that by additionally creating an array and a hash.

Not so bad whilst the range is in the 100s of thousands but once you need a range in the 10s of millions or more, your going to run out of memory pretty quick in order to create those 30 values.

This will produce as many unique values (in a random order) as you wish to fetch for any range upto 4 billion, whilst never consuming more than 512MB. (and considerably less for smaller ranges. eg. 0-100,000 will use < 13kB.)

```sub uniqRands {
state \$vec = '';
\$vec = '' if @_ == 2;
my \$n;
1 while vec( \$vec, \$n = int( rand \$_[0] ), 1 );
vec( \$vec, \$n, 1 ) = 1;
return \$n;
}

my @sample = map uniqRands( 100_000 ), 1 .. 30;

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

Replies are listed 'Best First'.
Re^2: Non-Repetitive Random Numbers
by FloydATC (Deacon) on Apr 05, 2013 at 13:34 UTC
What, you're limited to 0..4294967295, this sucks!

Just kidding, this solution is awesome :-)

-- Time flies when you don't know what you're doing

Create A New User
Node Status?
node history
Node Type: note [id://1027135]
help
Chatterbox?
and all is quiet...

How do I use this? | Other CB clients
Other Users?
Others making s'mores by the fire in the courtyard of the Monastery: (7)
As of 2018-06-19 20:54 GMT
Sections?
Information?
Find Nodes?
Leftovers?
Voting Booth?
Should cpanminus be part of the standard Perl release?

Results (114 votes). Check out past polls.

Notices?