>>>>> Simon Urbanek <simon.urba...@r-project.org>
>>>>> on Sun, 6 Feb 2011 20:53:01 -0500 writes:
> On Feb 6, 2011, at 8:10 PM, Paul Murrell wrote:
>> Hi
>>
>> On 3/02/2011 1:23 p.m., Simon Urbanek wrote:
>>>
>>> On Feb 2, 2011, at 7:00 PM, Paul Murrell wrote:
>>>
>>>> Hi
>>>>
>>>> Martin Maechler wrote:
>>>>> On Wed, Feb 2, 2011 at 23:30, Simon
>>>>> Urbanek<simon.urba...@r-project.org> wrote:
>>>>> On Feb 1, 2011, at 8:16 PM, Paul Murrell wrote:
>>>>>
>>>>>>> Hi
>>>>>>>
>>>>>>> On 2/02/2011 2:03 p.m., Henrik Bengtsson wrote:
>>>>>>>> On Tue, Feb 1, 2011 at 4:46 PM, Paul
>>>>>>>> Murrell<p.murr...@auckland.ac.nz> wrote:
>>>>>>>>> Hi
>>>>>>>>>
>>>>>>>>> On 1/02/2011 9:22 p.m., Martin Maechler wrote:
>>>>>>>>>>>>>>> Henrik Bengtsson<h...@biostat.ucsf.edu> on
>>>>>>>>>>>>>>> Mon, 31 Jan 2011 11:16:59 -0800 writes:
>>>>>>>>>>> Hi, str() on raster objects fails for certain
>>>>>>>>>>> dimensions. For example:
>>>>>>>>>>
>>>>>>>>>>>> str(as.raster(0, nrow=1, ncol=100)) 'raster'
>>>>>>>>>>>> chr [1, 1:100]
>>>>>>>>>>> "#000000" "#000000" "#000000" "#000000" ...
>>>>>>>>>>
>>>>>>>>>>>> str(as.raster(0, nrow=1, ncol=101)) Error in
>>>>>>>>>>>> `[.raster`(object,
>>>>>>>>>>> seq_len(max.len)) : subscript out of bounds
>>>>>>>>>>
>>>>>>>>>>> This seems to do with how str() and "[.raster"()
>>>>>>>>>>> is coded; when subsetting as a vector, which
>>>>>>>>>>> str() relies on, "[.raster"() still returns a
>>>>>>>>>>> matrix-like object, e.g.
>>>>>>>>>>
>>>>>>>>>>>> img<- as.raster(1:25, max=25, nrow=5, ncol=5);
>>>>>>>>>>>> img[1:2]
>>>>>>>>>>> [,1] [,2] [,3] [,4] [,5] [1,] "#0A0A0A"
>>>>>>>>>>> "#3D3D3D" "#707070" "#A3A3A3" "#D6D6D6" [2,]
>>>>>>>>>>> "#141414" "#474747" "#7A7A7A" "#ADADAD"
>>>>>>>>>>> "#E0E0E0"
>>>>>>>>>>
>>>>>>>>>>> compare with:
>>>>>>>>>>
>>>>>>>>>>>> as.matrix(img)[1:2]
>>>>>>>>>>> [1] "#0A0A0A" "#3D3D3D"
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>> The easy but incomplete fix is to do:
>>>>>>>>>>
>>>>>>>>>>> str.raster<- function(object, ...) {
>>>>>>>>>>> str(as.matrix(object), ...); }
>>>>>>>>>>
>>>>>>>>>>> Other suggestions?
>>>>>>>>>>
>>>>>>>>>> The informal "raster" class is behaving
>>>>>>>>>> ``illogical'' in the following sense:
>>>>>>>>>>
>>>>>>>>>>> r<- as.raster(0, nrow=1, ncol=11)
>>>>>>>>>>> r[seq_along(r)]
>>>>>>>>>> Error in `[.raster`(r, seq_along(r)) : subscript
>>>>>>>>>> out of bounds
>>>>>>>>>>
>>>>>>>>>> or, here equivalently,
>>>>>>>>>>> r[1:length(r)]
>>>>>>>>>> Error in `[.raster`(r, 1:length(r)) : subscript
>>>>>>>>>> out of bounds
>>>>>>>>>>
>>>>>>>>>> When classes do behave in such a way, they
>>>>>>>>>> definitely need their own str() method.
>>>>>>>>>>
>>>>>>>>>> However, the bug really is in "[.raster":
>>>>>>>>>> Currently, r[i] is equivalent to r[i,] which is
>>>>>>>>>> not at all matrix-like and its help clearly says
>>>>>>>>>> that subsetting should work as for matrices. A
>>>>>>>>>> recent thread on R-help/R-devel has mentioned the
>>>>>>>>>> fact that "[" methods for matrix-like methods
>>>>>>>>>> need to use both nargs() and missing() and that
>>>>>>>>>> "[.dataframe" has been the example to follow
>>>>>>>>>> "forever", IIRC already in S and S-plus as of 20
>>>>>>>>>> years ago.
>>>>>>>>> The main motivation for non-standard behaviour
>>>>>>>>> here is to make sure that a subset of a raster
>>>>>>>>> object NEVER produces a vector (because the
>>>>>>>>> conversion back to a raster object then produces a
>>>>>>>>> single-column raster and that may be a
>>>>>>>>> "surprise"). Thanks for making the code more
>>>>>>>>> standard and robust.
>>>>>>>>>
>>>>>>>>> The r[i] case is still tricky. The following
>>>>>>>>> behaviour is quite convenient ...
>>>>>>>>>
>>>>>>>>> r[r == "black"]<- "white"
>>>>>>>>>
>>>>>>>>> ... but the next behaviour is quite jarring (at
>>>>>>>>> least in terms of the raster image that results
>>>>>>>>> from it) ...
>>>>>>>>>
>>>>>>>>> r2<- r[1:(nrow(r) + 1)]
>>>>>>>>>
>>>>>>>>> So I think there is some justification for further
>>>>>>>>> non-standardness to try to ensure that the subset
>>>>>>>>> of a raster image always produces a sensible
>>>>>>>>> image. A simple solution would be just to outlaw
>>>>>>>>> r[i] for raster objects and force the user to
>>>>>>>>> write r[i, ] or r[, j], depending on what they
>>>>>>>>> want.
>>>>>>>> FYI, I've tried out Martin's updated version at it
>>>>>>>> seems like a one-column raster matrix is now
>>>>>>>> returned for r[i], e.g.
>>>>>>> Yes, that's what I've been looking at ...
>>>>>>>
>>>>>>>>> r<- as.raster(1:8, max=8, nrow=2, ncol=4); r
>>>>>>>> [,1] [,2] [,3] [,4] [1,] "#202020" "#606060"
>>>>>>>> "#9F9F9F" "#DFDFDF" [2,] "#404040" "#808080"
>>>>>>>> "#BFBFBF" "#FFFFFF"
>>>>>>>>
>>>>>>>>> r[1:length(r)]
>>>>>>>> [,1] [1,] "#202020" [2,] "#404040" [3,] "#606060"
>>>>>>>> [4,] "#808080" [5,] "#9F9F9F" [6,] "#BFBFBF" [7,]
>>>>>>>> "#DFDFDF" [8,] "#FFFFFF"
>>>>>>> ... and the above is exactly the sort of thing that
>>>>>>> will fry your mind if the image that you are
>>>>>>> subsetting is, for example, a photo.
>>>>>>>
>>>>> Why doesn't raster behave consistently like any matrix
>>>>>>> object?
>>>>> I would expect simply
>>>>>
>>>>>>> r[1:length(r)]
>>>>> [1] "#202020" "#404040" "#606060" "#808080" "#9F9F9F"
>>>>>>> "#BFBFBF"
>>>>> "#DFDFDF" [8] "#FFFFFF"
>>>>>
>>>>> Where it's obvious what happened. I saw the comment about
>>>>>>> the
>>>>> vector but I'm not sure I get it - why don't you want a
>>>>>>> vector?
>>>>> The raster is no different than matrices - you still need
>>>>>>> to
>>>>> define the dimensions when going back anyway, moreover
>>>>>>> what you
>>>>> get now is not consistent at all since there raster never
>>>>>>> had
>>>>> that dimension anyway ...
>>>>>
>>>>> Cheers, Simon
>>>>> I agree that this would be the most "logical" and
>>>>> notably least surprising behavior, which I find the
>>>>> most important argument (I'm sorry my last message was
>>>>> cut off as it was sent accidentally before being
>>>>> finished completely).
>>>>
>>>> I think this behaviour might surprise some ...
>>>>
>>>> download.file("http://cran.r-project.org/Rlogo.jpg";,
>>>> "Rlogo.jpg") library(ReadImages) logo<-
>>>> read.jpeg("Rlogo.jpg")
>>>>
>>>> rLogo<- as.raster(logo) rLogoBit<- rLogo[50:60, 50:60]
>>>>
>>>> library(grid) # Original image grid.raster(rLogoBit)
>>>> grid.newpage() # Subset produces a vector
>>>> grid.raster(rLogoBit[1:length(rLogoBit)])
>>>>
>>>
>> But this should fail IMHO since you're supplying a vector but
>>> grid.raster (assuming it's the same as rasterImage)
>>> requires a matrix - exactly as you would expect in the
>>> matrix case - if a function requires a matrix and you
>>> pass a vector, it will bark. I think you are explaining
>>> why going to vector *is* desirable ;). In the current
>>> case it simply generates the wrong dimensions instead of
>>> resulting in a vector, right?
>>
>> The raster subsetting always produces a raster, but
>> grid.raster() works with vectors anyway because
>> as.raster() has a vector method.
>>
> Well, isn't that the actual problem? ;) It could make sense but it
> should fail if dimensions are not specified for exactly the reason you
> mentioned - it is fatal if what you have is really an image ...
> Cheers, Simon
>> Anyway, I'm happy to go with things as they now are. I
>> think at worst it will encourage people to specify two
>> indices when subsetting a raster object, and that's not a
>> bad thing.
>>
>> Paul
I and (maybe others) are getting a bit lost..
AFAIK:
- Simon proposes that r[i] should return a simple character vector
such that raster images behave more naturally like matrices.
- Paul seems happy with r[i] returning a (k x 1) raster object
-- where k almost completely unrelated to the original
dim(r) -- with the argument that raster subsetting must always
return a "raster".
My vote would be for Simon's proposal, hence raster subsetting
should return a raster only when [i,j] or [i,] or [,j] syntax
is used.
Martin
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