On Sun, Feb 19, 2017 at 3:01 PM, David Winsemius <dwinsem...@comcast.net> wrote: > >> On Feb 19, 2017, at 11:37 AM, C W <tmrs...@gmail.com> wrote: >> >> Hi R, >> >> I am a little confused by the data.table package. >> >> library(data.table) >> >> df <- data.frame(w=rnorm(20, -10, 1), x= rnorm(20, 0, 1), y=rnorm(20, 10, 1), >> z=rnorm(20, 20, 1)) >> >> df <- data.table(df) > > df <- setDT(df) is preferred.
Don't you mean just setDT(df) ? setDT() modifies by reference. >> >> df_3 <- df[, a := x-y] # created new column a using x minus y, why are we >> using colon equals? > > You need to do more study of the extensive documentation. The behavior of the > ":=" function is discussed in detail there. You can get to that documentation with ?":=" Hadley -- http://hadley.nz ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
