R help - Apr 2021 - graphics useRaster check_irregular definition for date or posix

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]]

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 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]]
> 
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-- 
Dr Paul Murrell
Department of Statistics
The University of Auckland
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