Confused about using data.table package,
On Feb 20, 2017, at 8:12 AM, Hadley Wickham <h.wickham at gmail.com> wrote: On Sun, Feb 19, 2017 at 3:01 PM, David Winsemius <dwinsemius at comcast.net> wrote:
On Feb 19, 2017, at 11:37 AM, C W <tmrsg11 at 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