How can one generate all possible permutations of r elements out of n where r<n?

supriyoch_2008 has asked for the wisdom of the Perl Monks concerning the following question:

Hi PerlMonks,

It might be a silly question. But I donot find a simple perl code to solve this problem. I have an array like @a=qw/A B C D/; and I'm interested to get all possible permutations of say 3 elements out of 4 in the array and their total numbers i.e. 4p3=4!/(4-3)!=24 permutations along with 4 other uniform permutations (i.e. AAA,BBB, CCC,DDD). Thus total number of permutations will be 24+4=28. I need the permutations like ABC,ABD,BCD .. DDD and their total numbers (28). I have gone through some posts but nowhere I find the answer to this type of basic question. May I request the Perlmonks to provide suggestions for this problem? I am sure that I have put a very silly question. Moreover, the code must work for permutations of 2 or 4 elements out of 4 i.e. 4p2 and 4p4 along with their uniform permutations with little change in the code.

Comment on How can one generate all possible permutations of r elements out of n where r<n?

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Re: How can one generate all possible permutations of r elements out of n where r<n? by BrowserUk (Patriarch) on Feb 26, 2013 at 12:29 UTC
`C:\test>perl -MAlgorithm::Combinatorics=variations -E"$i=variations( [ +'A'..'D'], 3 ); say @$_ while $_= $i->next" ABC ABD ACB ACD ADB ADC BAC BAD BCA BCD BDA BDC CAB CAD CBA CBD CDA CDB DAB DAC DBA DBC DCA DCB` [download] 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.	[reply] [d/l]
Re^2: How can one generate all possible permutations of r elements out of n where r<n? by supriyoch_2008 (Monk) on Feb 27, 2013 at 09:11 UTC
Hi BrowserUK, Thank you very much for the code. But I am sorry that I do not understand the code as it does not start with #!/usr/bin/perl, the code I am a little acquainted with. With regards.	[reply]
Re^3: How can one generate all possible permutations of r elements out of n where r<n? by marto (Cardinal) on Feb 27, 2013 at 09:21 UTC
perlintro, perlrun, http://learn.perl.org. Update: you claim this code solved your problem, yet it didn't include `#!/usr/bin/perl`	[reply] [d/l]
Re: How can one generate all possible permutations of r elements out of n where r<n? by space_monk (Chaplain) on Feb 26, 2013 at 13:44 UTC
A very fast look on CPAN reveals Math::Combinatorics Despite the low version number, it looks as though it does what you want, and if it doesn't the source code is probably a good starting point to modify to do it. IIRC a lot of advice round here advises Googling and checking CPAN, because it's probably been asked before :-). A Monk aims to give answers to those who have none, and to learn from those who know more.	[reply]
Re^2: How can one generate all possible permutations of r elements out of n where r<n? by supriyoch_2008 (Monk) on Feb 27, 2013 at 09:14 UTC
Hi space_monk, Thanks for the suggestions. I have used Math::Combinatorics to solve the problem of combinations of elements. With kind regards.	[reply]
Re: How can one generate all possible permutations of r elements out of n where r<n? by daxim (Curate) on Feb 26, 2013 at 12:31 UTC
"uniform permutations" don't exist, at least not what you describe. Your number 4 is just the count of the elements of the input again, one does not need any algorithm to arrive at that conclusion.	[reply]
Re^2: How can one generate all possible permutations of r elements out of n where r<n? by supriyoch_2008 (Monk) on Feb 27, 2013 at 09:18 UTC
Hi daxim, Thanks for providing the information. It is true that uniform permutations don't exist. I used the term since I could not gather the appropriate term for permuations like AAA,TTT,GGG,CCC etc. With regards	[reply]
Re: How can one generate all possible permutations of r elements out of n where r<n? by Anonymous Monk on Feb 26, 2013 at 12:07 UTC
Several of your previous posts are on this style of topic, you "donot find a simple perl code", don't just search, try to write it yourself. Solve the problem with paper and pen, then convert to perl.	[reply]