Hi: dt[, mean(A), by = 'B'] B V1 [1,] 1 1.000000 [2,] 2 1.666667 [3,] 3 2.333333 [4,] 4 3.000000
...and I can see you've found the data.table mailing list... HTH, Dennis On Fri, Dec 3, 2010 at 3:38 PM, Santosh Srinivas <santosh.srini...@gmail.com > wrote: > Hello Group, > > I need a modification in the data.table example to get my intended > result shown below ... is there a more simple way! > > dt <- data.table(A = rep(1:3, each=4), B = rep(1:4, each=3), C = rep(1:2, > 6)) > dt[, transform(.SD,D=mean(A)), by="B"] > > > The result I want is below ... which is probably long winded! > > data.table(unique(as.data.frame(dt[, transform(.SD,D=mean(A)), > by="B"][,list(B,D)]))) > B D > [1,] 1 1.000000 > [2,] 2 1.666667 > [3,] 3 2.333333 > [4,] 4 3.000000 > > Thank you. > > ______________________________________________ > 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. > [[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.