Sorry, there may be some lingo for describing the extraction problem I have, but I don't know it.
I have a matrix of 2 rows and N columns, and a vector of N 1s and 2s. Matrix M: 1 2 3 4 ... N 1 A C D G ... 2 B D F H ... Vector v: 1 2 2 1 2 1 1 ... N I'd like to apply v to M to get Vector w: A D F G ... I.e. each element of v is interpreted as a row-index used to extract that row's value from the corresponding column in M into the corresponding column of w. Also eventually nrow(M) > 2, in which case the value of the elements of v would range over 1:nrow(M). Seems it should be simple, but maybe not? Thanks! Doug PS : I originally posted this on "R devel", then realized my mistake. "Move thread" didn't work when I tried it, though. -- View this message in context: http://www.nabble.com/How-to-extract-from-a-matrix-based-on-indices-in-a-vector--tp23967316p23967316.html Sent from the R help mailing list archive at Nabble.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.