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

[Martin Maechler]

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).
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
>>>>>
>>>>> ______________________________________________