[Rd] stats::line() does not produce correct Tukey line when n mod 6 is 2 or 3

[Joris Meys]

Can confirm this in R 3.4.0 :

end <- 6:100
res <- lapply(end, function(i) line(1:i,1:i))
absresid <- sapply(res, function(i) mean(abs(resid(i))))
plot(absresid, type = "h")
coefs <- sapply(res, coef)
plot(coefs[1,], coefs[2,])

> sessionInfo()
R version 3.4.0 (2017-04-21)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

Matrix products: default

locale:
[1] LC_COLLATE=English_United Kingdom.1252  LC_CTYPE=English_United
Kingdom.1252
[3] LC_MONETARY=English_United Kingdom.1252
LC_NUMERIC=C
[5] LC_TIME=English_United Kingdom.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

loaded via a namespace (and not attached):
[1] compiler_3.4.0 tools_3.4.0




On Sun, May 28, 2017 at 3:28 AM, GlenB <glnbrntt at gmail.com> wrote:

> Bug: stats::line() does not produce correct Tukey line when n mod 6 is 2 or
> 3
>
> Example: line(1:9,1:9) should have intercept 0 and slope 1 but it gives
> intercept -1 and slope 1.2
>
> Trying line(1:i,1:i) across a range of i makes it clear there's a cycle of
> length 6, with four of every six correct.
>
> Bug has been present across many versions.
>
> The machine I just tried it on just now has R3.2.3:
>
>                _
> platform       x86_64-w64-mingw32
> arch           x86_64
> os             mingw32
> system         x86_64, mingw32
> status
> major          3
> minor          2.3
> year           2015
> month          12
> day            10
> svn rev        69752
> language       R
> version.string R version 3.2.3 (2015-12-10)
> nickname       Wooden Christmas-Tree
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>



-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Mathematical Modelling, Statistics and Bio-Informatics

tel :  +32 (0)9 264 61 79
Joris.Meys at Ugent.be
-------------------------------
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