[R] problems subsetting

[Steve Lianoglou]

Hi,

On Thu, Nov 18, 2010 at 10:25 AM, Martin Tomko <martin.tomko at geo.uzh.ch> wrote:
> Hi Gerrit,
> indeed, that works. Excellent tip!
>
> For reference, I did this:
>
> subset1<-subset(summarystats,(Type==1)&(Class==1)&(Category==1))
>
> I am still not totally sure when one uses "&" amd when "&&"  - I was under
> the impression that && stands for logical AND....

If you can't find the appropriate documentation, try to experiment in
your workspace:

R> c(TRUE, TRUE, FALSE, TRUE) & c(FALSE, TRUE, TRUE, TRUE)
[1] FALSE  TRUE FALSE  TRUE

R> c(TRUE, TRUE, FALSE, TRUE) && c(FALSE, TRUE, TRUE, TRUE)
[1] FALSE

The single logical operators (& , |) run over the entire length of
your logical vectors.
The doubles (&&, ||) just evaluate the first element of the vectors,
and ignore the rest.

-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact