graphics useRaster check_irregular definition for date or posix

Hi Paul

Thanks for the FAQs related to the unwanted white lines. However, even 
if it is just the png/pdf viewer that causes the white lines, I would 
like to try to avoid them as much as possible, and setting useRaster to 
true does that.

My wish would be that I can use a date or POSIX* vector as x and/or y 
axis as it is without using some numerical values instead and then 
always need to take special care for the corresponding labels. 
Particularly for date/POSIX* objects this can be annoying. So the axes 
or their labels are not my problem, I just need the useRaster true or 
false decision to be consistent.

How do you deduce that the diff of the midpoints (i.e. the modifided x) 
is not "regular"? This, again, will be decided later in image.default() 
by check_irregular(), what brings us back to my initial post?

Cheers,
Chris

Am 15.04.2021 03:26 schrieb Paul Murrell:

Hi

Feeding R-help back in, in case my suggestions might be of use to someone else ...

Thanks for the examples - so the main benefit you are looking for is the labelling on the axes (date labels) ?

If you are just trying to avoid the annoying white lines, it may just be your PNG/PDF viewer;  see ...

http://cran.stat.auckland.ac.nz/doc/FAQ/R-FAQ.html#Why-are-there-unwanted-borders  <http://cran.stat.auckland.ac.nz/doc/FAQ/R-FAQ.html#Why-are-there-unwanted-borders>

Even so, making this work for date values for x/y seems like a useful thing.  However, ...

Neither your "fix" nor my "fix" actually works for the example that you have provided.  It just reveals another problem within image.default(), which is the calculation of "midpoints" ...

     if (length(x) > 1 && length(x) == nrow(z)) { # midpoints
         dx <- 0.5*diff(x)
         x <- c(x[1L] - dx[1L], x[-length(x)] + dx,
                x[length(x)] + dx[length(x)-1])
     }

This calculation does NOT produce the desired result for "Date"s (the diff() of the resulting modified 'x' is no longer regular).

So this needs a bit more thought - let me know if you come up with a fix for that calculation before me :)

Paul

On 15/04/21 4:05 am,cdanek at posteo.de  <mailto:cdanek at posteo.de>  wrote:

Hi Paul Thanks for your answer. I just answer to you, I dont know if 
this is correct (also the maillist?) x <- y <- 
seq(as.Date("2020-1-1"), as.Date("2020-12-31"), l=12) z <- 
array(rnorm(length(x)*length(y)), c(length(x), length(y))) image(x, 
y, z, useRaster=FALSE) # ok image(x, y, z, useRaster=TRUE) # error: 
'useRaster = TRUE' can only be used with a regular grid x <- y <- 
seq_len(12) image(x, y, z, useRaster=FALSE) # ok image(x, y, z, 
useRaster=TRUE) # ok The difference is the plot quality: useRaster = 
TRUE yields better quality as it omits strange white lines (in both 
png and pdf). I did not find a pattern when those white lines appear 
and when not. Hence, I cannot provide a reproducable example in which 
you can see the differences induced by the useRaster argument. In 
simple examples like the one above there is no difference between 
useRaster true and false plots. Do you have a suggestion on how to 
continue? Thanks a lot, Chris Am 14.04.2021 04:37 schrieb Paul Murrell:

Hi I doubt it is intended (to deliberately exclude "difftime" 
objects). Can you please supply a full image() example (with 'x' 
and/or 'y' as Dates and a 'z') ? So that I can see what ... image(x, 
y, z, useRaster=FALSE) ... looks like, so I can see what you want 
... image(x, y, z, useRaster=TRUE) ... to look like. I also wonder 
whether switching to ... dx[1][rep(1, length(dx))] ... might be 
better than switching to ... as.numeric(dx) It produces the same 
result for "difftime" objects, and may have a better chance of 
working better with other objects (although I confess that not 
having thought of using a "difftime" for 'x' I am also failing to 
think of further possibilities for 'x'). Paul On 14/04/21 3:11 
am,cdanek at posteo.de <mailto:cdanek at posteo.de> 
<mailto:cdanek at posteo.de <mailto:cdanek at posteo.de>> wrote:

Hi The function `check_irregular()` defined within 
`graphics::image.default()` checks if the `useRaster` argument for 
`graphics::image()` can be true or must be false. According to this 
function, the following example vector is irregular: ``` time <- 
seq(as.Date("2020-1-1"), as.Date("2020-12-31"), l=12) 
check_irregular(time, time) # TRUE ``` In my view, this is not 
correct. In this case, the `all.equal`-call does not evaluate to 
true due to the special class of `dx` (or `dy`). If I slightly 
rewrite the function as ``` my_check_irregular <- function (x, y) { 
dx <- as.numeric(diff(x)) dy <- as.numeric(diff(y)) (length(dx) && 
!isTRUE(all.equal(dx, rep(dx[1], length(dx))))) || (length(dy) && 
!isTRUE(all.equal(dy, rep(dy[1], length(dy))))) } ``` the correct 
answer is obtained (i.e. that the input vector is not irregular 
based on the rational behind `all.equal`): ``` 
my_check_irregular(time, time) # FALSE ``` The same applies to 
POSIX* objects. I was wondering if this is intended or not? Thanks 
a lot for any answer, Chris [[alternative HTML version deleted]]