[datatable-help] Subsetting with logical

[Arunkumar Srinivasan]

Michael,

I agree a note in the documentation should make things clearer. Thanks for
the post.
Matt has already written a bit on this change
here<http://r.789695.n4.nabble.com/Indexing-by-a-logical-column-td4665153.html#a4665142>
on
a post from GSee.

Have filed a request so that we don't forget.
https://r-forge.r-project.org/tracker/?func=detail&atid=5356&aid=5643&group_id=240



On Sat, Apr 26, 2014 at 4:19 AM, Michael Smith <my.r.help at gmail.com> wrote:

> A.K.,
>
> Thanks a lot for the link.
>
> Looking at `?data.table`, maybe the documentation could be changed to
> read something like this, with the text in bracket added:
>
> integer and logical vectors work the same way they do in
> \code{\link{[.data.frame}} (but see the \dQuote{Advanced} note below
> about an exception for single variable names).
>
> The thing is that I did read the documentation, but I stopped reading at
> that point because it said to expect the same behavior as with
> data.frame, which is not what happened in my example code. And based on
> your link to SO, other people have had the same issue too.
>
> M
>
>
> On 04/26/2014 09:15 AM, arun wrote:
> > Hi M,
> >
> > Check this link:
> >
> http://stackoverflow.com/questions/16191083/subset-data-table-by-logical-column
> >
> > A.K.
> >
> >
>
>
> On 04/26/2014 09:08 AM, Michael Smith wrote:> Here's another example,
> maybe more to the point. Shouldn't the second
> > line also work, since `b` is logical already?
> >
> > DT <- data.table(a = 1:8, b = c(TRUE, FALSE))
> > DT[b]               # Doesn't work.
> > DT[identity(b)]     # Does work.
> >
>
>
> >
> > On Friday, April 18, 2014 7:53 AM, Michael Smith <my.r.help at gmail.com>
> wrote:
> > Hi All,
> >
> > This is about subsetting using logicals. The code below is
> > self-explanatory (I hope). Is this a bug or a feature?
> >
> > Thanks,
> >
> > M
> >
> >
> >> DT <- data.table(a = 1:8, b = c(TRUE, FALSE))
> >> ## This does *not* work, but it should (in my humble opinion).
> >> DT[b]
> > Error in eval(expr, envir, enclos) : object 'b' not found
> >> ## This does work, but seems a bit awkward, given that b is already
> >> ## logical.
> >> DT[b == TRUE]
> >    a    b
> > 1: 1 TRUE
> > 2: 3 TRUE
> > 3: 5 TRUE
> > 4: 7 TRUE
> >> ## With data.frame things work as expected.
> >> DF <- as.data.frame(DT)
> >> DF[DF$b, ]
> >   a    b
> > 1 1 TRUE
> > 3 3 TRUE
> > 5 5 TRUE
> > 7 7 TRUE
> >> sessionInfo()
> > R version 3.0.2 (2013-09-25)
> > Platform: x86_64-redhat-linux-gnu (64-bit)
> >
> > locale:
> > [1] LC_CTYPE=en_US.utf8       LC_NUMERIC=C
> > LC_TIME=en_US.utf8
> > [4] LC_COLLATE=en_US.utf8     LC_MONETARY=en_US.utf8
> > LC_MESSAGES=en_US.utf8
> > [7] LC_PAPER=en_US.utf8       LC_NAME=C                 LC_ADDRESS=C
> >
> > [10] LC_TELEPHONE=C            LC_MEASUREMENT=en_US.utf8
> > LC_IDENTIFICATION=C
> >
> > attached base packages:
> > [1] stats     graphics  grDevices utils     datasets  methods   base
> >
> > other attached packages:
> > [1] data.table_1.9.2 colorout_1.0-1
> >
> > loaded via a namespace (and not attached):
> > [1] plyr_1.8.1     Rcpp_0.11.1    reshape2_1.2.2 stringr_0.6.2
> > _______________________________________________
> > datatable-help mailing list
> > 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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