Re: COMBIN

[Andreas Guelzow <aguelzow pyrshep ca>]

For a sheet function it would probably be better to implement an  
algorithm that creates the lexicographically ith combination, ie  
COMBIN_I(n,i).

Andreas

A J Guelzow


On 2010-07-31, at 8:31, Erich Neuwirth <erich neuwirth univie ac at>  
wrote:

> An algorithm which could easily implemented as a worksheet function  
> is the following:
>
> How to compute the lexicographically next combination from a given  
> combination
> (k taken from n):
> a) If the rightmost number in the row is  less than n, create a new  
> combination
> keeping all the numbers to the left of it and increasing the  
> rightmost number by 1.
> b) If the rightmost number is n, search the rightmost number whose  
> right neighbor
> is at least this number + 2. Increase this number by 1 and complete  
> the row by
> number+2, number+3 until you have a row with k numbers.
> If no such number exists, there is no next combination.
>
> Start with 1,2,3..k and compute the next combination for each  
> combination
>
> Example (3 out of 5)
>
> 1,2,3: 3<5, therefore rule a applies, next is 1,2,4
> 1,2,4: 4<5, therefore rule a applies, next is 1,2,5
> 1,2,5: apply rule b). 2<5, therefore 2 can be increased, next is 1,3,4
>
> 3,4,5
> No way of creating a next combination, so this is the last one.
>
>
>
>
>
>
>
>
>
>
> On Jul 31, 2010, at 3:31 PM, Prof. John C Nash wrote:
>
> > Slightly off-gnumeric, R (www.r-project.org) with which Gnumeric  
> > has had friendly exchanges, can do the job:
> >
> > > combn(5,2)
> >    [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
> > [1,]    1    1    1    1    2    2    2    3    3     4
> > [2,]    2    3    4    5    3    4    5    4    5     5
> > >
> >
> > In the past there were some ways to call R from Gnumeric, but I  
> > fear they are not currently functional, buy welcome correction on  
> > that.
> >
> > John Nash
> >
> > On 10-07-31 08:00 AM, gnumeric-list-request gnome org wrote:
> > > Date: Fri, 30 Jul 2010 11:02:35 -0400
> > > From: Morten Welinder<mortenw gnome org>
> > > To: yannis yannis<yanniscfu gmail com>
> > > Cc: gnumeric-list gnome org
> > > Subject: Re: COMBIN
> > > Message-ID:
> > >    <AANLkTindhzApAg5ROvvxX4oJea5BZeT9zMprp3G6CuF- mail gmail com>
> > > Content-Type: text/plain; charset=ISO-8859-1
> > >
> > > > Is there any way to know which are these combinations?
> > > > Any advise could be very helpful. Thank you for your time!
> > >
> > > Not via Gnumeric, but http://en.wikipedia.org/wiki/Combination
> > > is a good start.  Note the first external reference:
> > > http://compprog.wordpress.com/2007/10/17/generating-combinations-1/
> > >
> > > Morten
> > _______________________________________________
> > gnumeric-list mailing list
> > gnumeric-list gnome org
> > http://mail.gnome.org/mailman/listinfo/gnumeric-list
>
> --
> Erich Neuwirth, University of Vienna
> Faculty of Computer Science
> Center for Computer Science Didactics and Learning Research
> Visit our SunSITE at http://sunsite.univie.ac.at
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