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

[Duncan Murdoch]

On 28/04/2023 6:18 a.m., Achim Zeileis wrote:
> 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?

I agree that the two changes solve this problem.  I couldn't spot any 
other places that would need fixing.

Duncan Murdoch

> 
>> 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.
>>
> ______________________________________________
> 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.