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

[Achim Zeileis]

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.

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
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>> 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.
>