http://www.perlmonks.org?node_id=219491

huskey has asked for the wisdom of the Perl Monks concerning the following question:

What I need is to give a list of members a random number selected from an array of numbers. For example if there were 200 members in my list, each member would get a randomly selected number between 1 and 200, and once a member had that number it would be removed from the array of numbers, so that each member has a unique random number. Does that make sense? What would be the easiest way to do this?

Replies are listed 'Best First'.
Re: random number
by traveler (Parson) on Dec 13, 2002 at 08:30 UTC
You can just shuffle the list. Use
``` use Algorithm::Numerical::Shuffle qw /shuffle/;
@shuffled = shuffle (1..100);
or
``` @shuffled = shuffle (3,7,19,1000,44);
You can also shuffle a list in place.

HTH, --traveler

Re: random number
by BrowserUk (Pope) on Dec 13, 2002 at 03:53 UTC

Take a look at this earlier post Re: unique random numbers and the thread it's in. It should get you started.

Examine what is said, not who speaks.

Re: random number
by insensate (Hermit) on Dec 13, 2002 at 04:08 UTC
Here's a snippit that will initialize an array and select a number while the array still has elements...what you do with the element is up to you...
```use strict;
my \$max = 200;                                #number of elements for
+array
my @array = (0..\$max-1);                      #initialize array
while(@array !=0){
my \$index   = rand @array;                  #pick a random element o
+f the existing array
my \$element = \$array[\$index];               #extract the element
my @newarray = grep {\$_ !=\$element} @array; #remove the element
@array = @newarray;                         #reset the array
}
Addendum: See BrowserUk's reply for a more tidy/efficient method of extracting the element from the array

Given that you know the index of the item you want to remove from the array, it would be much more efficient to use splice instead of grep to remove the item from the array.

```#replace
my @newarray = grep {\$_ !=\$element} @array; #remove the element
#with
splice @array, \$index, 1; #remove item from array;
# and remove this. No need as the array has been modified.
# @array = @newarray;             #reset the array

Examine what is said, not who speaks.

```#splice is still O(n)
\$array[\$index] = \$array[-1];
pop @array;
```perl -le '@a=1..200; print while \$_ = splice @a, rand @a, 1'
```-sauoq