[Rd] [.raster bug {was "str() on raster objects fails .."}

Simon Urbanek simon.urbanek at r-project.org
Mon Feb 7 02:53:01 CET 2011 

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.urbanek at 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.murrell at auckland.ac.nz>   wrote:
>>>>>>>> Hi
>>>>>>>> 
>>>>>>>> On 1/02/2011 9:22 p.m., Martin Maechler wrote:
>>>>>>>>>>>>>> Henrik Bengtsson<hb at 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
> 
> 
>> Cheers, Simon
>> 
>> 
>> 
>> 
>> 
>>> Paul
>>> 
>>>> Martin
>>>>>> Paul
>>>>>> 
>>>>>>>> r[1:5,drop=TRUE]
>>>>>>> [,1] [1,] "#202020" [2,] "#404040" [3,] "#606060" [4,]
>>>>>>> "#808080" [5,] "#9F9F9F" Warning message: In `[.raster`(r,
>>>>>>> 1:5, drop = TRUE) : 'drop' is always implicitly FALSE in
>>>>>>> '[.raster'
>>>>>>> 
>>>>>>> Also,
>>>>>>> 
>>>>>>>> r[1:5]<- "white" r
>>>>>>> [,1]    [,2]    [,3]      [,4] [1,] "white" "white" "white"
>>>>>>> "#DFDFDF" [2,] "white" "white" "#BFBFBF" "#FFFFFF"
>>>>>>> 
>>>>>>> /Henrik
>>>>>>> 
>>>>>>>> Paul
>>>>>>>> 
>>>>>>>>> Thank you, Henrik, for the bug report. Martin
>>>>>>>>> 
>>>>>>>>> ______________________________________________
>>> 
>>> -- Dr Paul Murrell Department of Statistics The University of
>>> Auckland Private Bag 92019 Auckland New Zealand 64 9 3737599
>>> x85392 paul at stat.auckland.ac.nz
>>> http://www.stat.auckland.ac.nz/~paul/
>>> 
>>> 
>> 
> 
> -- 
> Dr Paul Murrell
> Department of Statistics
> The University of Auckland
> Private Bag 92019
> Auckland
> New Zealand
> 64 9 3737599 x85392
> paul at stat.auckland.ac.nz
> http://www.stat.auckland.ac.nz/~paul/
> 
>

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