[R] Extracting vectors from matrices

[Anon.]

There is probably a simple and obvious answer to this, so sorry for
wasting your time...

I have a matrix of predictions from an proportional odds model (using
the polr function in MASS), so the columns are the probabilities of the
responses, and the rows are the data points.  I have another column with
the observed responses, and I want to extract the probabilities for the
observed responses.

As a toy example, if I have 
x <- matrix(c(1,2,3,4,5,6),2,3)
y <- c(1,3)
and I want to extract the numbers in x[1,1] and x[2,3] (the columns
being indexed from y), what do I do?

Bob

-- 
Bob O'Hara
Metapopulation Research Group
Division of Population Biology
Department of Ecology and Systematics
PO Box 17 (Arkadiankatu 7)
FIN-00014 University of Helsinki
Finland

tel: +358 9 191 7382  fax: +358 9 191 7301 
email: bob.ohara at helsinki.fi
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