[perl-python] combinatorics fun

[Xah Lee]

a year ago i wrote this perl program as part of a larger program.

as a exercise of fun, let's do a python version. I'll post my version
later today.

=pod

combo(n) returns a collection with elements of pairs that is all
possible combinations of 2 things from n. For example, combo(4)
returns {'3,4' => ['3',4],'1,2' => [1,2],'1,3' => [1,3],'1,4' =>
[1,4],'2,3' => ['2',3],'2,4' => ['2',4]}; Hash form is returned
instead of array for this program.

=cut

sub combo ($) {
my $max=$_[0];
my %hh=();
for (my $j=1; $j < $max; ++$j) {
for (my $i=1; $i <= $max; ++$i) {
my $m = (($i+$j)-1)%$max+1;
if ($i < $m){ $hh{"$i,$m"}=[$i,$m];}
}
}
return \%hh;
}


use Data:umper;
$Data:umper::Indent=0;
print Dumper combo(5);


This is Perl-Python a-day. To subscribe, see
http://xahlee.org/perl-python/python.html

Xah
(e-mail address removed)
http://xahlee.org/PageTwo_dir/more.html

 

[David Eppstein]

combo(n) returns a collection with elements of pairs that is all
possible combinations of 2 things from n. For example, combo(4)
returns {'3,4' => ['3',4],'1,2' => [1,2],'1,3' => [1,3],'1,4' =>
[1,4],'2,3' => ['2',3],'2,4' => ['2',4]}; Hash form is returned
instead of array for this program.

def combo(n):
return dict([('%d,%d'%(i,j),(i,j))
for j in range(n) for i in range(j)])

import pprint
pprint.pprint(combo(5))


output:

{'0,1': (0, 1),
'0,2': (0, 2),
'0,3': (0, 3),
'0,4': (0, 4),
'1,2': (1, 2),
'1,3': (1, 3),
'1,4': (1, 4),
'2,3': (2, 3),
'2,4': (2, 4),
'3,4': (3, 4)}


Note I'm using 0-based indexing, use range(1,n+1) and range(1,j+1)
instead if you really need it to be 1-based.

Also I'm using Python 2.3, I think in 2.4 you can take out the square
brackets and it would still work.

 

[Jack Diederich]

a year ago i wrote this perl program as part of a larger program.

as a exercise of fun, let's do a python version. I'll post my version
later today.

from probstat import Combination

There is something deeply wrong about plugging your own module when
responding to a troll.

-Jack

ps, Foxtrot Oscar Alpha Delta

 

[axel]

a year ago i wrote this perl program as part of a larger program.

sub combo ($) {
my $max=$_[0];
my %hh=();
for (my $j=1; $j < $max; ++$j) {
for (my $i=1; $i <= $max; ++$i) {
my $m = (($i+$j)-1)%$max+1;
if ($i < $m){ $hh{"$i,$m"}=[$i,$m];}
}
}
return \%hh;
}

Well, it's not obfuscated Perl. It is, however, an obfuscated algorithm.

Sane people would use something along the lines of:

sub combo {
my $max = shift;
my %hh=();
for my $i ( 1 .. $max ) {
for my $j ( $i + 1 .. $max ) {
$hh{"$i,$j"} = [$i, $j];
}
}
return \%hh;
}


Axel

 

[YYUsenet]

a year ago i wrote this perl program as part of a larger program.

as a exercise of fun, let's do a python version. I'll post my version
later today. [code snipped]

This is Perl-Python a-day. To subscribe, see
http://xahlee.org/perl-python/python.html

Xah
(e-mail address removed)
http://xahlee.org/PageTwo_dir/more.html

Why are you posting this to comp.lang.python? This obviously has nothing
to do with python at all. If you are trying to teach people python,
claiming that "...let's do a python version. I'll post my version later
today." Isn't really the proper way to do it. An even better method
would be to set up a website dedicated to nothing but it, and stop
posting here with garbage code that no one wants to read, and that helps
no one. Please, consider others a little bit when you go off on your
wild hope that you might be able to teach other people what you
obviously know nothing about, teaching people from a language that you
know nothing about. *PLEASE STOP POSTING*!! *NOBODY WANTS YOU TO POST*!!

 

[Haibao Tang]

I am no longer resisting. As time goes, the nausea when I first saw Mr.
Lee's smelly "technical posts" is starting to fade. The discussion
group should have a high tolerance towards polymorphic people these
days.

 

[Xah Lee]

David Eppstein's code is very nice.

Here's the python version of the perl code:

©# -*- coding: utf-8 -*-
©# Python
©
©def combo (n):
© '''returns all possible (unordered) pairs out of n numbers 1 to
n.
©
© Returns a dictionary. The keys are of the form "n,m",
© and their values are tuples. e.g. combo(4) returns
© {'3,4': (3, 4), '1,4': (1, 4), '1,2': (1, 2),
© '1,3': (1, 3), '2,4': (2, 4), '2,3': (2, 3)}'''
© result={}
© for j in range(1,n):
© for i in range(1,n+1):
© m = ((i+j)-1) % n + 1
© if (i < m):
© result["%d,%d"%(i,m)]=(i,m)
© return result
©
©print combo(4)

So sweet.

Xah
(e-mail address removed)
http://xahlee.org/PageTwo_dir/more.html

 

[bruno modulix]

Xah Lee wrote:
(snip insanities)

Why are you posting this to comp.lang.python? This obviously has nothing
to do with python at all. If you are trying to teach people python,
claiming that "...let's do a python version. I'll post my version later
today." Isn't really the proper way to do it. An even better method
would be to set up a website dedicated to nothing but it, and stop
posting here with garbage code that no one wants to read, and that helps
no one. Please, consider others a little bit when you go off on your
wild hope that you might be able to teach other people what you
obviously know nothing about, teaching people from a language that you
know nothing about. *PLEASE STOP POSTING*!! *NOBODY WANTS YOU TO POST*!!

The guy is an obvious, well-known and self-proclaimed troll. Dont feed
the troll.