[R-Forge #2110] Add . and .. symbol prefixes and inherits=FALSE for strict scope

[arunsrinivasan]

Submitted by: Matt Dowle; Assigned to: Nobody; R-Forge link

inherits=FALSE would allow user to specify that j should use column names only, and if column name doesn't exist that should be error rather than possibly finding a match in calling scope.

..() is for the sub-join examples where the join goes in j and you want to refer to the columns in i not .SD. Something like that.

[mattdowle]

would be useful here :
http://stackoverflow.com/questions/34077955/variable-usage-in-data-table

[JoshOBrien]

Once version 10.2 is released (if not before), we should revisit this answer to remove the mention of datatable.WhenJisSymbolThenCallingScope=TRUE. (As always, any of you should feel free to edit as you like).

[Synergist]

It'd be nice to be able to use this feature and the ! notation for excluding columns in tandem.

dt <- data.table(x = 1:10, y = rnorm(10), z = runif(10))
cols <- c('y', 'z')
dt[, !..cols] # should return col x

[ctbrown]

I followed the SO issue here looking for this feature. Since, it is still experimental may I recommend that the syntax be changed from ..A to ..$A where .. is a reference to the parent.frame. I believe this is more R-like, does the same thing and conforms to user expectations. It seems that this can be simply(?) done with:

makeActiveBinding('..', parent.frame)

[arunsrinivasan]

Refer to #2186 for name mention under NEWS.

[franknarf1]

Another SO post: https://stackoverflow.com/q/45387223/