[Rd] Subsetting row in single column matrix drops names in resulting vector

[Serguei Sokol]

Le 22/11/2018 à 14:47, Emil Bode a écrit :
> The problem is that the drop is only applied (or not) after the subsetting, so what R does is:
> - Getting the subset, which means a 1 x 1 matrix.
> - Only then It either returns that as is (when drop=FALSE), or removes ALL dimensions of extent 1, regardless of whether these are rows or columns (or higher dimensions).
> And it can't keep any names, because what name should be returned? The name 'row1' is just as valid as 'col1'.
If it is the only reason to not return any name in this case, I could 
make a suggestion.
Let return the name corresponding to the index in subsetting request, 
i.e. for a one-column matrix example it would give

names(a[1,])
#"row1"
names(a[2,])
#"row2"

as the indexes 1 and 2 here above corresponds to rows.

Just my 0.02€
Serguei.


> I guess if we could design everything anew, a solution would be to be able to specify something like a[1,,drop='row'], or a[1,,drop=1] to drop the rows but keep columns, and get a vector being equal to 'row1' (which in this case just has length-1, and names 'col1')
> That not how it's designed, but you could use 'adrop()' from the 'abind' package:
> abind:: adrop(a[1,,drop=FALSE], drop=1) first subsets, then drops the row-dimension, so gives what you're looking for.
> Hope this solves your problem.
>
> Best regards,
> Emil Bode
>   
>
> On 21/11/2018, 17:58, "R-devel on behalf of Dmitriy Selivanov" <r-devel-bounces using r-project.org on behalf of selivanov.dmitriy using gmail.com> wrote:
>
>      Hi Rui. Thanks for answer, I'm aware of drop = FALSE option. Unfortunately
>      it doesn't resolve the issue - I'm expecting to get a vector, not a matrix .
>      
>      ср, 21 нояб. 2018 г. в 20:54, Rui Barradas <ruipbarradas using sapo.pt>:
>      
>      > Hello,
>      >
>      > Use drop = FALSE.
>      >
>      > a[1, , drop = FALSE]
>      > #     col1
>      > #row1    1
>      >
>      >
>      > Hope this helps,
>      >
>      > Rui Barradas
>      >
>      > Às 16:51 de 21/11/2018, Dmitriy Selivanov escreveu:
>      > > Hello here. I'm struggling to understand R's subsetting behavior in
>      > couple
>      > > of edge cases - subsetting row in a single column matrix and subsetting
>      > > column in a single row matrix. I've read R's docs several times and
>      > haven't
>      > > found answer.
>      > >
>      > > Consider following example:
>      > >
>      > > a = matrix(1:2, nrow = 2, dimnames = list(c("row1", "row2"), c("col1")))
>      > > a[1, ]
>      > > # 1
>      > >
>      > > It returns *unnamed* vector `1` where I would expect named vector. In
>      > fact
>      > > it returns named vector when number of columns is > 1.
>      > > Same issue applicable to single row matrix. Is it a bug? looks very
>      > > counterintuitive.
>      > >
>      > >
>      >
>      
>      
>      --
>      Regards
>      Dmitriy Selivanov
>      
>      	[[alternative HTML version deleted]]
>      
>      ______________________________________________
>      R-devel using r-project.org mailing list
>      https://stat.ethz.ch/mailman/listinfo/r-devel
>      
>
>
> ______________________________________________
> R-devel using r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel


-- 
Serguei Sokol
Ingenieur de recherche INRA

Cellule mathématiques
LISBP, INSA/INRA UMR 792, INSA/CNRS UMR 5504
135 Avenue de Rangueil
31077 Toulouse Cedex 04

tel: +33 5 62 25 01 27
email: sokol using insa-toulouse.fr
http://www.lisbp.fr