[datatable-help] Bug report #5100 reg.

[Arunkumar Srinivasan]

Glad that we agree on better-ing the documentation. However, I don't find it a sound argument that we deviate from data.frame because the design is bad, *when we inherit from data.frame*. The choice is already made! Too many such trivial inconsistencies piles up pretty quickly and could potentially result in a steep learning curve - as there are different set of rules to be memorised.  

Tackling the point of "inheriting from data.frame", *but* this, this, this.. and many other things are different, if can't be avoided, should be *very clearly* documented (in the beginning, maybe as a cheat sheet) so that people aren't confused.


Arun


On Thursday, November 14, 2013 at 5:39 PM, Eduard Antonyan wrote:

> I agree that it's inconsistent with data.frame, and imo that's a good thing. We don't replicate the drop argument, so it wouldn't be possible to return a data.table when with=FALSE and either way drop=TRUE by default is a bad design choice in data.frame and matrix (that is unlikely to change given R-core's attitude towards that type of a thing).
> 
> I'm always pro more and better documentation :)
> 
> 
> On Thu, Nov 14, 2013 at 10:33 AM, Arunkumar Srinivasan <aragorn168b at gmail.com (mailto:aragorn168b at gmail.com)> wrote:
> > Eddi, At the least, I think the documentation needs to be clearer on the use of "with=FALSE". It does feel inconsistent with the fact that "j" with a single column should return a vector. In data.frames, the type in "j" being column names, if it's just one column name, would return a vector, unless drop = FALSE. That is, DF[, "y"] will return a vector while DF[, c("x", "y")] will return a data.frame. So, it is inconsistent with data.frame here, I think. 
> > 
> > 
> > Arun
> > 
> > 
> > On Thursday, November 14, 2013 at 5:25 PM, Eduard Antonyan wrote:
> > 
> > > 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 (mailto: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
> > > > 
> > > > 
> > > > _______________________________________________
> > > > datatable-help mailing list
> > > > datatable-help at lists.r-forge.r-project.org (mailto:datatable-help at lists.r-forge.r-project.org)
> > > > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
> > > 
> > 
> 

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