R help - May 2005 - Intersection of more than two groups in one function?

Hi all,

As far as I can tell, the only canned way to do an intersect between two 
vectors of ints is the intersect(vec1, vec2) function -- is there another 
function I'm missing for intersecting more than two vectors??

TIA,
Ken

Here's a brute-force approach:
> "%i%" <- intersect
> x1 <- c(1, 3, 4, 7)
> x2 <- c(3, 7, 8)
> x3 <- c(7, 1)
> x1 %i% x2 %i% x3
[1] 7

Andy
> From: Ken Termiso
> 
> Hi all,
> 
> As far as I can tell, the only canned way to do an intersect 
> between two 
> vectors of ints is the intersect(vec1, vec2) function -- is 
> there another 
> function I'm missing for intersecting more than two vectors??
> 
> TIA,
> Ken
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
> 
> 
>

No, I know of no "canned" way to do it, as it's based on match(),
which is
for two vectors only.

A brute force loop to do it is simple, as I suspect you realize. Perhaps a
faster way is to use tabulate() to find values that appear n times (for n
vectors). That is:

## assume your integer vectors are components of a list, mylist.

## warning: not tested
bigvec<-unlist(mylist)
sort(unique(bigvec))[tabulate(bigvec)==length(mylist)]



-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Ken Termiso
> Sent: Thursday, May 05, 2005 1:15 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Intersection of more than two groups in one function?
> 
> Hi all,
> 
> As far as I can tell, the only canned way to do an intersect 
> between two 
> vectors of ints is the intersect(vec1, vec2) function -- is 
> there another 
> function I'm missing for intersecting more than two vectors??
> 
> TIA,
> Ken
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>