[datatable-help] := and ':=" throwing errors

[Cron Acronis]

On Sun, 20 Mar 2016 22:55:33 -0700, carlsutton wrote:

> My goal is to create proportions for several variables, by group, and
> save these in new columns.   So far I have spent most of the day
> researching this, retaking the Data Camp data table course, and all
> iterations have failed miserably.   Several google searches were not
> helpful.  Console out put (code and error messages below.  Hopefully.
> Proportions.R
> <http://r.789695.n4.nabble.com/file/n4718825/Proportions.R>
> <http://r.789695.n4.nabble.com/file/n4718825/Capture.png>
> 
> Carl Sutton
> 
> 
> 
> -----
> Carl Sutton

Try this:

dt1[, ':='(propta = sum(a)/.N, propt.b = sum(b)/.N), by = c]