At 10:01 09.07.2009, SIES 73 wrote:
I've also had several use cases where I needed
"cell-like" attributes, that is, attributes that
have the same dimensions as the original array
and are subsetted in the same way --along all its dimensions.
So we're talking about a way to add metadata to
matrices/arrays at 3 possible levels:
1) at the "whole object" level:
attributes that are not dropped on subsetting
2) at the "dimension" level: attributes
that behave like "dimnames", i.e. subsetted along each dimension
3) at the "cell" level: attributes that
are subsetted in the same way as the original array
My proposal would be simpler that Tony's
suggestion: like "dimnames", just have reserved
attribute names for each case, say "objdata",
"dimdata", and "celldata" (or "objattr", "dimattr" and "cellattr").
If "objattr", "dimattr" and "cellattr" are lists,
they would offer save places for all attributes
that should be kept on subsetting. In my view
this would be very useful, because that way a
general solution for data description, like
variabel names, variable labels, units, ... could be reached.
On the other hand, Tony's pattern would allow as
many attributes of each type as necessary (some
multiplicity is already possible with the
simpler design as dimdata or celldata could be
lists of lists), at the cost of a more complex
scheme of attributes that needs to be "parsed" each time.
On Tony's suggestion, "attr.keep.on.subset" and
"attr.dimname.like" (and possible
"attr.cell.like") could be kept on a single list
with 3 elements, something like:
> attr(x, "attr.subset.with") <- list(object=..., dims=..., cells=...)
Would something like this make sense for R-core
--either for standard arrays or as a new class--
or would it be better implemented in a package?
Enrique
-----Original Message-----
From: Tony Plate [mailto:tpl...@acm.org]
Sent: miércoles, 08 de julio de 2009 18:01
To: r-devel@r-project.org
Cc: Bengoechea Bartolomé Enrique (SIES 73); Henrik Bengtsson
Subject: Re: [Rd] Suggestion: Dimension-sensitive attributes
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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> https://stat.ethz.ch/mailman/listinfo/r-devel
>
>
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