R help - Mar 2010 - Working with combinations

I am working with the combinations function (available in the gtools package). 
However, rather than store all of the possible combinations I would like to
check each combination to see if it meets a certain criteria.  If it does, I
will then store it.

I have looked at the combinations code but am unsure where in the algorithm I
would be able to operate on each combination.

Thanks!


      
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I think there are several packages that implement combinations and several
that allow you to specify a function  to be called when each vector of
combinations
is generated.  I can't recall the names of all such packages, but the
Combinations package on www.omegahat.org/Combinations is one.

 D.

Herm Walsh wrote:
> I am working with the combinations function (available in the gtools
package).  However, rather than store all of the possible combinations I would
like to check each combination to see if it meets a certain criteria.  If it
does, I will then store it.
> 
> I have looked at the combinations code but am unsure where in the algorithm
I would be able to operate on each combination.
> 
> Thanks!
> 
> 
>       
> 	[[alternative HTML version deleted]]
> 
> 
> 
> ------------------------------------------------------------------------
> 
> ______________________________________________
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> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

On Mar 2, 2010, at 9:15 PM, Herm Walsh wrote:
> I am working with the combinations function (available in the gtools  
> package).  However, rather than store all of the possible  
> combinations I would like to check each combination to see if it  
> meets a certain criteria.  If it does, I will then store it.
>
> I have looked at the combinations code but am unsure where in the  
> algorithm I would be able to operate on each combination.
Logical indexing:

 > combinations(3,2,letters[1:3])[,1]=="a"
[1]  TRUE  TRUE FALSE

 > combinations(3,2,letters[1:3])[ combinations(3,2,letters[1:3])[, 
1]=="a", ]
      [,1] [,2]
[1,] "a"  "b"
[2,] "a"  "c"

-- 
David Winsemius.