http://qs1969.pair.com?node_id=11140589

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

I'm looking at Algorithm::Permute and it doesn't seem to have this feature: given an array of say 8 items, how can I list all permutations of length 5, not the full 8?

• Comment on Getting permutations of length n of an array of length greater than n?

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Re: Getting permutations of length n of an array of length greater than n?
by pryrt (Monsignor) on Jan 18, 2022 at 22:15 UTC
As shown in the Algorithm::Permute synopsis, if you want r elements out of the n objects in each permutation,
```# but also you can create r of n objects permutation generator, where
+r <= n
my \$p = Algorithm::Permute->new([1..4], 3);

A practical example is shown here, where there are n=4 objects and I take groups of r=2:

```C:\usr\local\share>perl -MAlgorithm::Permute -e "my \$p=Algorithm::Perm
+ute::->new([1..4],2); while(my @res=\$p->next){print qq(@res\n)}"
2 1
1 2
3 2
2 3
3 1
1 3
4 2
2 4
4 3
3 4
4 1
1 4

Your example would be ...->new([1..8],5) to get permutations of length 5 from the 8 objects given. Or

```C:\usr\local\share>perl -MAlgorithm::Permute -e "my \$p=Algorithm::Perm
+ute::->new([1..8],5); while(my @res=\$p->next){print qq(@res\n)}"
5 4 3 2 1
4 5 3 2 1
4 3 5 2 1
4 3 2 5 1
4 3 2 1 5
5 3 4 2 1
3 5 4 2 1
3 4 5 2 1
3 4 2 5 1
3 4 2 1 5
...
8 1 2 3 4
1 8 2 3 4
1 2 8 3 4
1 2 3 8 4
1 2 3 4 8

Thanks! I've got it working now.

What I failed at was comprehending the CPAN documentation, but you have to admit "you can create r of n objects permutation generator, where r <= n" is a little obscurely worded!

Re: Getting permutations of length n of an array of length greater than n?
by choroba (Archbishop) on Jan 18, 2022 at 22:08 UTC
Re: Getting permutations of length n of an array of length greater than n?
by tybalt89 (Prior) on Jan 18, 2022 at 22:42 UTC

Alternate way

```#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11140589
use warnings;
use ntheory qw( forcomb forperm );

forcomb
{
my @sel = @_;
forperm { print @sel[@_], ' ' } scalar @sel;
} 8, 5;
print "\n";