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
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