This _was_ in the answer you got, but to clarify things, perhaps try this: (M <- matrix(1:9,3,3)) (ix <- rbind(c(3,2),c(1,3))) M[3,2] M[1,3] M[ix]
-pd On 19 Jun 2014, at 14:12 , carol white <wht_...@yahoo.com> wrote: > The extracted values don't form a matrix and that's the question how to > extract because which returns the indexes? that is, from > 1,1 > 2,1 > 1,2 > > how to retrieve values? > > Or if at the position 2,1, there is a negative value, how to retrieve > 1,1 > 1,2 > > > > Carol > > > > On Thursday, June 19, 2014 1:29 PM, Bart Kastermans <kaste...@kasterma.net> > wrote: > > > > On 19 Jun 2014, at 13:19, carol white <wht_...@yahoo.com> wrote: > >> Hi, >> Is there a way to extract a subset of non-contiguous elements of a matrix >> elegantly and with 1 or very few scripts? >> >> Suppose I have a matrix of positive and negative numbers (m) and I want to >> retrieve only the positive number. This I can do >> >> which(m>0, arr.ind=T) which gives the indices of positive elements like >> (37,1), (80,1), ..., (54,2) etc. How can I extract positive numbers without >> looping on the indexes provided by which to make a new matrix? > > What matrix do you want? For e.g. > >> tm.1 <- matrix(c(11,22,33,-4), ncol=2) >> which(tm.1 > 0, arr.ind=TRUE) > row col > [1,] 1 1 > [2,] 2 1 > [3,] 1 2 >> tm.1[which(tm.1 > 0, arr.ind=TRUE)] > [1] 11 22 33 > > The extracted values do not form a matrix. > > Either the above contains the answer, or I don’t understand the question. > > Best, > Bart > > >> >> thanks, >> >> Carol > [[alternative HTML version deleted]] > > ______________________________________________ > 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. -- Peter Dalgaard, Professor Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd....@cbs.dk Priv: pda...@gmail.com ______________________________________________ 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.
