I'll try to make a list of places where data.table != data.frame operation.
Arun On Thursday, November 14, 2013 at 5:46 PM, Arunkumar Srinivasan wrote: > 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 > > <[email protected] (mailto:[email protected])> 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 > > > > <[email protected] (mailto:[email protected])> 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 > > > > > [email protected] > > > > > (mailto:[email protected]) > > > > > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help > > > > > > > > > >
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