I think you are looking for mt[cbind(vt, seq_along(vt))]
which uses some trickines known as matrix indexing (basically, the two columns created by cbind() are considered row & col indices -- then seq_along() gives the col1,col2, bit as needed. HTH, Michael On Tue, Jun 12, 2012 at 10:28 AM, Zhenjiang Lan <lan.zhenji...@gmail.com> wrote: > here's my question: suppose I have a matrix: > > mt<-matrix(1:12,ncol=6) > > now I have a vector > > vt<-c(1,2,2,2,1,2) > > which means I want to get: > the 1st row for column1; > the 2nd row for column2; > the 2nd row for column3; > the 2nd row for column4; > ... > > that what I want is this vector: > 1,4,6,8,9,12 > > Does anyone know how to do this fast? > I know I can use for-loop to travel all columns,but that's not what I want. > > ______________________________________________ > 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. ______________________________________________ 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.
