[datatable-help] Bug report #5100 reg.

[Eduard Antonyan]

DT[, y] returning a vector is I think the only correct behavior, given the
understanding of j-expression as something evaluated in the DT environment.
If they want a data.table they should simply use DT[, list(y)] or DT[,
data.table(y)].

I haven't thought about DT[, "y", with = FALSE] before as I pretty much
never use that form, but I see an argument for it staying as is, because
"y" and c("y") are the same and since we all presumably agree that DT[,
c("y", "z"), with = FALSE] should return a data.table. If DT[, c("y"), with
= FALSE] returned a different type that would mean inconsistent return
types which makes life much harder for users (as evidenced by the periodic
drop=FALSE questions that come up on SO).

Going back to DT[, y], note that y and list(y) actually produce *different*
results (in e.g. base_env), so there is no type consistency issue there
between DT[, y] and DT[, list(y, z)].


On Thu, Nov 14, 2013 at 6:09 AM, Arunkumar Srinivasan <aragorn168b at gmail.com
> wrote:

>  Hi everybody,
>
> It'd be nice if you could weigh-in on the bug report filed by Bill here:
>
> https://r-forge.r-project.org/tracker/index.php?func=detail&aid=5100&group_id=240&atid=975
>
> The gist of it is:
>
> require(data.table)
> DT <- data.table(x=1:5, y=6:10, z=11:15)
> DT[, y] # returns a vector
> DT[, "y", with=FALSE] # returns a data.table
>
> The question from the bug report basically is: "why is that in the first
> case, 'j' has only one column and we get a vector, but in the second case,
> we get a data.table?"
>
> My question is: Is this behaviour okay or do you prefer that the first one
> returns a data.table as well or the second one (with "with=FALSE") returns
> a vector?
>
> Thank you,
> Arun
>
>
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