R help - Aug 2002 - The unary - operator and matrix column labels

I am making some changes to the permax library (so that it will accept
NA's).  This function performs a permutation analysis to identify
discriminating attributes distinguishing two groups of observations.  It takes
the form (at its most simplistic):

permax(data, ig1)

where ig1 is one group of interest.  The other group (if not specified) is
assumed to be the remaining observations, namely, -ig1.

The problem is that I would like to be able to specify ig1 not as a vector of
numeric indicies, but as a vector of column labels (as specified by data <-
as.matrix(read.table("file", header=T....)).  But if I do this:

ig1 <- c('patient1', 'patient2')

then, while I can do this:

data[,ig1]

I can no longer do this:

data[,-ig1]

because the unary operator does not like working with column labels.  Is there a
way to go backwards and determine the column indices from the column labels, or
perhaps and even more simple way to obtain a vector of complementary column
labels given a subset of labels?

Thanks,
Eric



-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._

Kort, Eric <Eric.Kort at vai.org> writes:
>   ig1 <- c('patient1', 'patient2')
> then, while I can do this:
>   data[,ig1]
> I can no longer do this:
>   data[,-ig1]
> because the unary operator does not like working with column labels.  Is
> there a way to go backwards and determine the column indices from the
column
> labels...?
If you know "ig1" is indeed a column of the matrix "data",
this should work:

R> data[ , -match(ig1, colnames(data))]

If you don't know that for sure, and/or you want to preserve the matrix
structure of the result (drop=F), then here's a fancier version:

R> data[ , setdiff(colnames(data), ig1), drop=F]
-- 
                              -- David Brahm (brahm at alum.mit.edu)
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._