[R] Confused about using data.table package,

[David Winsemius]

> 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