[R] grDevices::hcl.colors using two colours: Bug or Feature?

[Achim Zeileis]

On Fri, 28 Apr 2023, Achim Zeileis wrote:

> This was introduced in 4.3.0 (hence Rui cannot reproduce it in 4.2.3).
>
> It's a bug and was introduced when fixing this other bug:
>
> https://bugs.R-project.org/show_bug.cgi?id=18476
> https://hypatia.math.ethz.ch/pipermail/r-help/2023-February/476960.html
>
> Apparently, it only affects the case with n = 2 for diverging and divergingx 
> palettes. The culprit is this line:
>
> i <- if(n2 == 1L) 0 else seq.int(1, by = -2/(n - 1), length.out = n2)
>
> I think n2 == 1L is not the right condition and we need to distinguish n = 1 
> and n = 2.

I think the solution is simply to use n == 1L instead of n2 == 1L, both in 
"diverging" (line 188 in hcl.colors.R) and "divergingx" (line 197).

Duncan, maybe you can have a look at this as well?

> Will have a closer look...
>
> Thanks for reporting this!
> Achim
>
> On Fri, 28 Apr 2023, Rui Barradas wrote:
>
>> Às 06:01 de 28/04/2023, Stevie Pederson escreveu:
>>> Hi,
>>> 
>>> I'm not sure if this is a bug or a feature, but after updating to Rv4.3, 
>>> if
>>> requesting two colours from hcl.colors() you now get the same colour 
>>> twice.
>>> This occurs for all palettes I've tried. My reprex:
>>> 
>>> hcl.colors(2, "Vik")
>>> [1] "#F1F1F1" "#F1F1F1"
>>> 
>>> As I have multiple workflows I run repeatedly with A vs B comparisons, 
>>> this
>>> has just broken the visualisations in many of them. Obviously a
>>> workaround is hcl.colors(3, "Vik")[c(1, 3)] but this seems rather
>>> unintuitive.
>>> 
>>> Thanks in advance,
>>> 
>>> Stevie
>>> 
>>> sessionInfo()
>>> R version 4.3.0 (2023-04-21)
>>> Platform: x86_64-pc-linux-gnu (64-bit)
>>> Running under: Ubuntu 20.04.6 LTS
>>> 
>>> Matrix products: default
>>> BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.9.0
>>> LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.9.0
>>> 
>>> locale:
>>>   [1] LC_CTYPE=en_AU.UTF-8       LC_NUMERIC=C
>>>   [3] LC_TIME=en_AU.UTF-8        LC_COLLATE=en_AU.UTF-8
>>>   [5] LC_MONETARY=en_AU.UTF-8    LC_MESSAGES=en_AU.UTF-8
>>>   [7] LC_PAPER=en_AU.UTF-8       LC_NAME=C
>>>   [9] LC_ADDRESS=C               LC_TELEPHONE=C
>>> [11] LC_MEASUREMENT=en_AU.UTF-8 LC_IDENTIFICATION=C
>>> 
>>> time zone: Australia/Adelaide
>>> tzcode source: system (glibc)
>>> 
>>> attached base packages:
>>> [1] stats     graphics  grDevices utils     datasets  methods   base
>>> 
>>> loaded via a namespace (and not attached):
>>> [1] compiler_4.3.0 tools_4.3.0
>>>
>>> 	[[alternative HTML version deleted]]
>>> 
>>> ______________________________________________
>>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide 
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>> Hello,
>> 
>> I cannot reproduce this on Windows.
>> 
>> 
>> hcl.colors(2, "Vik")
>> # [1] "#002E60" "#3E2000"
>> 
>> clrs <- sapply(hcl.pals(), \(p) hcl.colors(2, p))
>> any(apply(clrs, 2, \(x) x[1] == x[2]))
>> # [1] FALSE
>> 
>> sessionInfo()
>> # R version 4.2.3 (2023-03-15 ucrt)
>> # Platform: x86_64-w64-mingw32/x64 (64-bit)
>> # Running under: Windows 10 x64 (build 22621)
>> #
>> # Matrix products: default
>> #
>> # locale:
>> # [1] LC_COLLATE=Portuguese_Portugal.utf8 
>> LC_CTYPE=Portuguese_Portugal.utf8
>> # [3] LC_MONETARY=Portuguese_Portugal.utf8 LC_NUMERIC=C
>> # [5] LC_TIME=Portuguese_Portugal.utf8
>> #
>> # attached base packages:
>> # [1] stats     graphics  grDevices utils     datasets  methods   base
>> #
>> # loaded via a namespace (and not attached):
>> # [1] compiler_4.2.3
>> 
>> 
>> Hope this helps,
>> 
>> Rui Barradas
>> 
>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide 
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>> 
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>