[R] How to find a split point in a curve?

PIKAL Petr petr@p|k@| @end|ng |rom prechez@@cz
Fri May 15 09:15:06 CEST 2020


Hi

Maybe I am wrong but it seems to me that it is cumulative data from recent
epidemy in some state.

If yes, instead of inventing wheel I would go to canned and proved solution
using tools from
https://www.repidemicsconsortium.org/

I found useful and enlightening this blog especially first part from
February 18th.
https://timchurches.github.io/blog/

Cheers
Petr

> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Luigi Marongiu
> Sent: Thursday, May 14, 2020 5:12 PM
> To: r-help <r-help using r-project.org>
> Subject: [R] How to find a split point in a curve?
> 
> Dear all,
> I am trying to find a turning point in some data. In the initial phase,
the
> data increases more or less exponentially (thus it is linear in a nat log
> transform), then reaches a plateau. I would like to find the point that
> marks the end of the exponential phase.
> I understand that the function spline can build a curve; is it possible
> with it to find the turning points? I have no idea of how to use spline
> though.
> Here is a working example.
> Thank you
> 
> ```
> Y = c(259, 716, 1404, 2173, 3944, 5403, 7140, 9121,
>       11220, 13809, 16634, 19869, 23753, 27447,
>       30590, 33975, 36627, 39600, 42067, 44082,
>       58190, 63280, 65921, 67929, 69977, 71865,
>       73614, 74005, 74894, 75717, 76365, 76579,
>       77087, 77493, 77926, 78253, 78680, 79253,
>       79455, 79580, 79699, 79838, 79981, 80080,
>       80124, 80164, 80183, 80207, 80222, 80230,
>       80241, 80261, 80261, 80277, 80290, 80303,
>       80337, 80376, 80422, 80461, 80539, 80586,
>       80653, 80708, 80762, 80807, 80807, 80886,
>       80922, 80957, 80988, 81007, 81037, 81076,
>       81108, 81108, 81171, 81213, 81259, 81358,
>       81466, 81555, 81601, 81647, 81673, 81998,
>       82025, 82041, 82053, 82064, 82094, 82104,
>       82110, 82122, 82133, 82136, 82142, 82164,
>       82168, 82180, 82181, 82184, 82187, 82188,
>       82190, 82192, 82193, 82194)
> Y = log(Y)
> X = 1:length(Y)
> plot(Y ~ X, ylab = "Ln(Y)", xlim=c(0,10, main="zoomed in"))
> abline(lm(Y[1:3] ~ X[1:3]))
> abline(lm(Y[1:5] ~ X[1:5]), lty=2)
> text(7, 6, "After third or fifth point, there is deviance", pos=3)
> text(2.5, 10, "Solid line: linear model points 1:3", pos =3)
> text(2.5, 9, "Dashed line: linear model points 1:5", pos =3)
> plot(Y ~ X, ylab = "Ln(Y)", xlim=c(0,10, main="overall"))
> abline(lm(Y[1:3] ~ X[1:3]))
> ```
> 
> 	[[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.


More information about the R-help mailing list