> On Feb 20, 2017, at 8:12 AM, Hadley Wickham <h.wick...@gmail.com> wrote: > > 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.
Thanks for the correction. > >>> >>> 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 ?":=" That's a good place to start reading, but I was thinking of data.table::datatable-faq, data.table::datatable-intro which are on the Vignettes page from: help(pac=data.table). > > Hadley > > -- > http://hadley.nz David Winsemius Alameda, CA, USA ______________________________________________ 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.
