[Rd] Suggestion: Dimension-sensitive attributes

[Tony Plate]

There have been times when I've thought this could be useful too.

One way to go about it could be to introduce a special attribute that 
controls how attributes are dealt with in subsetting, e.g., 
"attr.dimname.like".  The contents of this would be character data; on 
subsetting, any attribute that had a name appearing in this vector would 
be treated as a dimension.  At the same time, it might be nice to also 
introduce "attr.keep.on.subset", which would specify which attributes 
should be kept on the result of a subsetting operation (could be useful 
for attributes that specify units).  This of course could be a way of 
implementing Henrik's suggestion: dimattr(x, "misc") <- value would add 
"misc" to the "attr.dimname.like" attribute and also set the attribute 
"misc".  The tricky part would be modifying the "[" methods.   However, 
the most useful would probably be the one for ordinary matrices and 
arrays, and others could be modified when and if their maintainers see 
the need.

-- Tony Plate

Bengoechea Bartolomé Enrique (SIES 73) wrote:
> Hi,
>
> I agree with Henrik that his suggestion to have "dimension vector attributes" working like dimnames (see below) would be an extremely useful infrastructure adittion to R.
>
> If this is not considered for R-core, I am happy to try to implement this in a package, as a new class. And possibly do the same thing for data frames. Should you have any comments, ideas or suggestions about it, please share!
>
> Best,
>
> Enrique
>
> -----------------------------------------------------------------------------
> Subject: 
> From: Henrik Bengtsson <hb_at_stat.berkeley.edu 
> Date: Sun, 07 Jun 2009 14:42:08 -0700
>
> Hi, 
>
> maybe this has been suggested before, but would it be possible, without not breaking too much existing code, to add other "dimension vector attributes" in addition to 'dimnames'? These attributes would then be subsetted just like dimnames. 
>
> Something like this: 
>
>   
>> x <- array(1:30, dim=c(2,3,5)) 
>> dimnames(x) <- list(c("a", "b"), c("a1", "a2", "a3"), NULL); 
>> dimattr(x, "misc") <- list(1:2, list(x=1:5, y=letters[1:8], z=NA), letters[1:5]); 
>>     
>
>
>   
>> y <- x[,1:2,2:3] 
>> str(dimnames(y)) 
>>     
>
> List of 3 
>
>  $ : chr [1:2] "a" "b"
>  $ : chr [1:2] "a1" "a2"
>  $ : NULL
>
>
>   
>> str(dimattr(x, "misc")) 
>>     
>
> List of 3 
>  $ : int [1:2] 1 2 
>  $ :List of 2 
>   ..$ x: int [1:5] 1 2 3 4 5 
>   ..$ y: chr [1:8] "a" "b" "c" "d" ... 
>  $ : chr [1:2] "b" "c" 
>
>  I can imagine this needs to be added in several places and functions such as is.vector() needs to be updated etc. It is not a quick migration, but is it something worth considering for the future? 
>
> /Henrik 
>
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