R devel - Oct 2005 - Inconsistency with matrix indexing (PR#8214)

Full_Name: Stefan Albrecht
Version: 2.2.0
OS: Windows XP
Submission from: (NULL) (194.127.2.74)


Dear all,

in the new R 2.2.0, the matrix indexing has been changed. In my opinion, this
leads to an inconsistency when indexing one-row matrices.
Take
> (mat <- matrix(1:9, nrow = 3, dimnames = list(paste("r", 1:3,
sep = ""),
paste("c", 1:3, sep = ""))))
   c1 c2 c3
r1  1  4  7
r2  2  5  8
r3  3  6  9

Now taking the first row of the first-row of mat preserves the column
names
> mat[1, , drop = FALSE][1, ]
c1 c2 c3 
 1  4  7 

This is not true for the first column of the first-row of
mat
> mat[1, , drop = FALSE][, 1]
[1] 1

However, for the first column of the first two rows of mat the row names are
retained
> mat[1:2, , drop = FALSE][, 1]
r1 r2 
 1  2 

This feature can lead to problems when indexing matrixes of different row
numbers, since the row names are not preserved in all cases.

I suggest to preseve the row names also for 
> mat[1, , drop = FALSE][, 1]
Would it be possible to implement this feature? Many thanks.

With best regards,

Stefan Albrecht

stefan.albrecht at allianz.com wrote:
> Full_Name: Stefan Albrecht
> Version: 2.2.0
> OS: Windows XP
> Submission from: (NULL) (194.127.2.74)
> 
> 
> Dear all,
> 
> in the new R 2.2.0, the matrix indexing has been changed.
I just tried your code in R 2.0.1 and 2.1.1, and got the same output as 
you did.  Which version are you comparing to?

Duncan Murdoch


  In my opinion, this
> leads to an inconsistency when indexing one-row matrices.
> Take
> 
>>(mat <- matrix(1:9, nrow = 3, dimnames = list(paste("r",
1:3, sep = ""),
> 
> paste("c", 1:3, sep = ""))))
>    c1 c2 c3
> r1  1  4  7
> r2  2  5  8
> r3  3  6  9
> 
> Now taking the first row of the first-row of mat preserves the column names
> 
>>mat[1, , drop = FALSE][1, ]
> 
> c1 c2 c3 
>  1  4  7 
> 
> This is not true for the first column of the first-row of mat
> 
>>mat[1, , drop = FALSE][, 1]
> 
> [1] 1
> 
> However, for the first column of the first two rows of mat the row names
are
> retained
> 
>>mat[1:2, , drop = FALSE][, 1]
> 
> r1 r2 
>  1  2 
> 
> This feature can lead to problems when indexing matrixes of different row
> numbers, since the row names are not preserved in all cases.
> 
> I suggest to preseve the row names also for 
> 
>>mat[1, , drop = FALSE][, 1]
> 
> 
> Would it be possible to implement this feature? Many thanks.
> 
> With best regards,
> 
> Stefan Albrecht
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

>>>>> "Duncan" == Duncan Murdoch <murdoch at
stats.uwo.ca>
>>>>>     on Tue, 18 Oct 2005 09:50:59 -0400 writes:
    Duncan> On 10/18/2005 9:32 AM, stefan.albrecht at allianz.com wrote:
    >> Dear Duncan,
    >> 
    >> you are right. In both R 2.2.0 and 2.1.1 you get the same result.
What has
    >> actually changed is the following:
    >> In R 2.1.1
    >>> mat[1, , drop = FALSE][1]
    >> r1 
    >> 1 
    >> 
    >> While in R 2.2.0
    >>> mat[1, , drop = FALSE][1]
    >> [1] 1

    Duncan> I don't agree with your suggestion.  mat[1, , drop = FALSE]
    Duncan> is a 1x3 matrix, with both row and column
    Duncan> names.  Indexing it by [1] says that you want to
    Duncan> treat it as a vector, and give the first element.
    Duncan> How could R know whether to keep the row or column
    Duncan> name for that [1,1] element?  What should it do with
    Duncan> the expression

    Duncan> mat[1,1 , drop = FALSE][1]

    Duncan> ?

    Duncan> If you are really concerned about the names, you should use
matrix
    Duncan> indexing in both places with drop = FALSE:

    >> mat[1, , drop = FALSE][1,1,drop=FALSE]
    Duncan> c1
    Duncan> r1  1

    Duncan> Duncan Murdoch

yes, definitely.  There's no bug here, and there was rather a
bug in previous behavior.

Just a simpler example {"for posteriority"}:
> (M <- cbind(a=0:1, b=c(A=2, B=3)))
  a b 
A 0 2
B 1 3
> M[1,2, drop=FALSE]
  b 
A 2
> M[1,2]
[1] 2
> M[2]  ### treat M as vector -> lose names
[1] 1
> M[2:3]
[1] 1 2
>