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

[Henrik Bengtsson]

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.

> 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"

> 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
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>
> --
> 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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