image() with all NAs fails (PR#8228)

On Thu, 20 Oct 2005 murdoch at stats.uwo.ca wrote:

On 10/20/2005 12:41 PM, barry.rowlingson at gmail.com wrote:

Full_Name: Barry Rowlingson
Version: 2.2.0
OS: Linux
Submission from: (NULL) (194.80.32.8)


The image function with a matrix of all NA values fails with:

xyz=list(x=1:3,y=1:4,z=matrix(NA,3,4))
image(xyz)

Error in image.default(xyz) : invalid z limits
In addition: Warning messages:
1: no finite arguments to min; returning Inf
2: no finite arguments to max; returning -Inf

Image can handle any number of NAs as long as there is at least one data value:

xyz=list(x=1:3,y=1:4,z=matrix(c(1,rep(NA,11)),3,4))
image(xyz)

and shows NAs as transparent. However if it is all NAs then the z-limit
calculation breaks down as above.

 It seems reasonable to me that image() with all NAs should produce a
completely transparent/empty image (after displaying the axes if add!=TRUE) and
not fail with an error.

I agree, though I think the warnings are reasonable and a fix shouldn't
remove them.  However, I'm not sure what the fix should be.  There's a
test in image.default

       if (any(!is.finite(zlim)) || diff(zlim) < 0)
           stop("invalid z limits")


that is throwing the error.  We want the error if a user specifies
diff(zlim) < 0 or non-finite z limits, we just don't want it if all the
z's are NA.  But a test all(is.na(z)) looks a bit expensive for such a
rare case.

It is not actually documented that zlim can be omitted (something we need 
to fix too).  Why not just add a check for zlim not being missing to that 
test?