Confused about using data.table package,
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.
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