Hi Sverre, On Tue, Aug 2, 2011 at 10:22 PM, Sverre Stausland <john...@fas.harvard.edu> wrote: > Dear helpers, > > I'm trying to extract certain rows from a matrix according to the > values the rows have in a certain column. I've been googling for a > while without result. > > Here's a reproducible example of a matrix (and the one I was playing > with initially): > >> myrepo<-getOption("repos") >> myrepo["CRAN"]<-"http://software.rc.fas.harvard.edu/mirrors/R/" >> class(available.packages(contriburl=contrib.url(myrepo))) > [1] "matrix" > > I can extract according to rows and column positions: > >> available.packages(contriburl=contrib.url(myrepo))[2,2] > [1] "0.1" > > But how can I extract the rows according to their values in a column, > when $ is not usable for vector matrices? Say I would like all the > rows where the value in the column "Version" is "0.1" (as above). For > a data frame, I would have done it like this: > >> available.packages(contriburl=contrib.url(myrepo))->avail.pack >> avail.pack[avail.pack$Version=="0.1",] > Error in avail.pack$Version : $ operator is invalid for atomic vectors
Use [ instead of $, like this: avail.pack[avail.pack[, "Version"] == "0.1", ] best, Ista > > Also, thanks to those who responded to my recent question in > https://stat.ethz.ch/pipermail/r-help/2011-August/285650.html (I > assume it's best not to respond at the end of threads with a "thank > you" only, to avoid cluttering people's inboxes?) > > best > Sverre > > ______________________________________________ > R-help@r-project.org mailing list > 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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ R-help@r-project.org mailing list 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.