[Rd] Antwort: Re: Inconsistency with matrix indexing (PR#8214)

[Duncan Murdoch]

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

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

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

?

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

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

Duncan Murdoch

> 
> In both cases
>> mat[1, , drop = FALSE]
>    c1 c2 c3
> r1  1  4  7
> 
> I would strongly prefer to retain the row index r1 above.
> Of course, you could argue that mat[1, , drop = FALSE][1] relates to the 
> column name c1. However, I think the lower dimension is a vector and this 
> typically a column with row names. Most likely, a  wiser and more concise 
> interpretation than the mine is necessary, but the problem of dropping and 
> loosing information is quite evident in any case.
> 
> Still, I believe, my suggestion below is justified. Things like this 
> happen quite often to me and it regularly takes time and effort to rectify 
> the problem.
> Retaining the matrix features in sames could really be an advantage and 
> avoid many if's and other workarounds.
> 
> Many thanks and best regards,
> Stefan
> 
> 
> 
> Duncan Murdoch <murdoch at stats.uwo.ca> 
> 2005-10-18 14:33
> 
> An
> stefan.albrecht at allianz.com
> Kopie
> r-devel at stat.math.ethz.ch, R-bugs at biostat.ku.dk
> Thema
> Re: [Rd] Inconsistency with matrix indexing (PR#8214)
> 
> 
> 
> 
> 
> 
> 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
>> 
>> ______________________________________________
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> 
> 
>