local maxima positions in a vector with duplicated values
Dear Bill, Bert, Greg and Abby, I tested your code (honestly apart from Abby's solution because it needed an additional package and I run R in a server which is not administrated by myself), they work and I found them equivalent. (Probably Bill's and Greg's solutions are a bit faster than Bert's.) In my real application I found a case where none of them work: when the series is monotonic. In this case the last number of the vector (or the last duplicated numbers) is not a maximum but it is anyway the highest number of the vector:
x <- c(1,1,1,2,2,3,4,4,4,5,6,6,6)
The error is: argument is of length zero.
Your code is at the moment too complicated for me to modify. I ask if there is an "easy" extension of the code that you kindly wrote for me to handle also this possibility.
Thank you for everything
Stefano
(oo)
--oOO--( )--OOo--------------------------------------
Stefano Sofia PhD
Civil Protection - Marche Region - Italy
Meteo Section
Snow Section
Via del Colle Ameno 5
60126 Torrette di Ancona, Ancona (AN)
Uff: +39 071 806 7743
E-mail: stefano.sofia at regione.marche.it
---Oo---------oO----------------------------------------
Da: Bill Dunlap [williamwdunlap at gmail.com]
Inviato: venerd? 26 marzo 2021 18.40
A: Stefano Sofia
Cc: r-help mailing list
Oggetto: Re: [R] local maxima positions in a vector with duplicated values
Using rle() may make it easier - finding the peak values is easier and
select from cumsum(lengths) to get the positions of the last values
before the peaks, then add 1. I have not tested the following very
much.
function(x) {
rx <- rle(x)
cumsum(rx$lengths)[c(diff(diff(rx$values)>0) == -1,FALSE,FALSE)]+1
}
-Bill
On Fri, Mar 26, 2021 at 8:36 AM Stefano Sofia
<stefano.sofia at regione.marche.it> wrote:
>
> Dear list users,
> I need to find local maxima and local minima positions in a vector where there might be duplicates; in the particular in case of
> - duplicated local maxima, I should take the position of the first duplicated value;
> - duplicated local minima, I should take the position of the last duplicated value.
>
> Example:
>
> >x <- c(1,0,0,0,2,2,3,4,0,1,1,0,5,5,5,0,1)
> >which(diff(diff(x)>=0)<0)+1
>
> gives me 8 11 15 while I need 8 10 13;
>
> >which(diff(diff(x)>0)>0)+1
>
> gives me 4 6 9 12 16 while I need 4 9 12 16.
>
> Could you please help me in this task? I would be happier not to use additional packages.
>
> Thank you for your precious help
> Stefano
>
>
> (oo)
> --oOO--( )--OOo--------------------------------------
> Stefano Sofia PhD
> Civil Protection - Marche Region - Italy
> Meteo Section
> Snow Section
> Via del Colle Ameno 5
> 60126 Torrette di Ancona, Ancona (AN)
> Uff: +39 071 806 7743
> E-mail: stefano.sofia at regione.marche.it
> ---Oo---------oO----------------------------------------
>
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