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local maxima positions in a vector with duplicated values

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Stefano Sofia

local maxima positions in a vector with duplicated values

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: [hidden email]
---Oo---------oO----------------------------------------

________________________________

AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere informazioni confidenziali, pertanto è destinato solo a persone autorizzate alla ricezione. I messaggi di posta elettronica per i client di Regione Marche possono contenere informazioni confidenziali e con privilegi legali. Se non si è il destinatario specificato, non leggere, copiare, inoltrare o archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso di necessità ed urgenza, la risposta al presente messaggio di posta elettronica può essere visionata da persone estranee al destinatario.
IMPORTANT NOTICE: This e-mail message is intended to be received only by persons entitled to receive the confidential information it may contain. E-mail messages to clients of Regione Marche may contain information that is confidential and legally privileged. Please do not read, copy, forward, or store this message unless you are an intended recipient of it. If you have received this message in error, please forward it to the sender and delete it completely from your computer system.

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[[alternative HTML version deleted]]

______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Bill Dunlap-2

Re: 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
<[hidden email]> 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: [hidden email]
> ---Oo---------oO----------------------------------------
>
> ________________________________
>
> AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere informazioni confidenziali, pertanto è destinato solo a persone autorizzate alla ricezione. I messaggi di posta elettronica per i client di Regione Marche possono contenere informazioni confidenziali e con privilegi legali. Se non si è il destinatario specificato, non leggere, copiare, inoltrare o archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso di necessità ed urgenza, la risposta al presente messaggio di posta elettronica può essere visionata da persone estranee al destinatario.
> IMPORTANT NOTICE: This e-mail message is intended to be received only by persons entitled to receive the confidential information it may contain. E-mail messages to clients of Regione Marche may contain information that is confidential and legally privileged. Please do not read, copy, forward, or store this message unless you are an intended recipient of it. If you have received this message in error, please forward it to the sender and delete it completely from your computer system.
>
> --
> Questo messaggio stato analizzato da Libraesva ESG ed risultato non infetto.
> This message was scanned by Libraesva ESG and is believed to be clean.
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] 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.

______________________________________________
[hidden email] 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.

Bert Gunter-2

Re: local maxima positions in a vector with duplicated values

In reply to this post by Stefano Sofia

WARNING: I have not carefully tested the following, so you will need to do
so before using.

Like Bill, I found rle a clearer approach. Here's my (not so elegant,
probably) version:

> x <-c(1,0,0,0,2,2,3,4,0,1,1,0,5,5,5,0,1)
> z <- rle(x)
> vals <- z$values
> n <- length(vals)
> whmin<-c(vals[-1], -Inf) > vals & c(-Inf, vals[-n]) > vals
> whmax <- c(vals[-1], Inf) < vals & c(Inf, vals[-n]) < vals
> cumsum(z$lengths)[whmin]
[1] 4 9 12 16
> cumsum(z$lengths)[whmax[-1]] +1
[1] 8 10 13

Cheers,
Bert
Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Fri, Mar 26, 2021 at 8:36 AM Stefano Sofia <
[hidden email]> 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: [hidden email]
> ---Oo---------oO----------------------------------------
>
> ________________________________
>
> AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere
> informazioni confidenziali, pertanto è destinato solo a persone autorizzate
> alla ricezione. I messaggi di posta elettronica per i client di Regione
> Marche possono contenere informazioni confidenziali e con privilegi legali.
> Se non si è il destinatario specificato, non leggere, copiare, inoltrare o
> archiviare questo messaggio. Se si è ricevuto questo messaggio per errore,
> inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio
> computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in
> caso di necessità ed urgenza, la risposta al presente messaggio di posta
> elettronica può essere visionata da persone estranee al destinatario.
> IMPORTANT NOTICE: This e-mail message is intended to be received only by
> persons entitled to receive the confidential information it may contain.
> E-mail messages to clients of Regione Marche may contain information that
> is confidential and legally privileged. Please do not read, copy, forward,
> or store this message unless you are an intended recipient of it. If you
> have received this message in error, please forward it to the sender and
> delete it completely from your computer system.
>
> --
> Questo messaggio stato analizzato da Libraesva ESG ed risultato non
> infetto.
> This message was scanned by Libraesva ESG and is believed to be clean.
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] 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.
>

[[alternative HTML version deleted]]

______________________________________________
[hidden email] 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.

Greg Minshall

Re: local maxima positions in a vector with duplicated values

In reply to this post by Stefano Sofia

Stefano,

my contribution is similar to Bill Dunlap's:

x <- c(1,0,0,0,2,2,3,4,0,1,1,0,5,5,5,0,1)
(cumsum(rle(x)$lengths)-(rle(x)$length-1))[which(diff(diff(rle(x)$values)>=0)<0)+1]
cumsum(rle(x)$lengths)[which(diff(diff(rle(x)$value)>0)>0)+1]

kind of a cute little problem, actually.

cheers, Greg

______________________________________________
[hidden email] 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.

aBBy Spurdle, ⍺XY

Re: local maxima positions in a vector with duplicated values

In reply to this post by Stefano Sofia

Hi Stefano,

My package, vectools, is partly designed for this purpose.
(Unfortunately, the package *is* subject to *change*, and some of the
functions may change in the next update).

library (vectools)
which.maxs (x, ret.type="intervals")[,1] # c (8, 10, 13)
which.mins (x, ret.type="intervals")[,2] # c (4, 9, 12, 16)

best,
B.

P.S.
I'll make sure the next version has an option for the lower/upper index.

On Sat, Mar 27, 2021 at 4:36 AM Stefano Sofia
<[hidden email]> wrote:

Stefano Sofia

Re: local maxima positions in a vector with duplicated values

In reply to this post by Bill Dunlap-2

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: [hidden email]
---Oo---------oO----------------------------------------

________________________________________
Da: Bill Dunlap [[hidden email]]
Inviato: venerdì 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
<[hidden email]> 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: [hidden email]
> ---Oo---------oO----------------------------------------
>
> ________________________________
>
> AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere informazioni confidenziali, pertanto è destinato solo a persone autorizzate alla ricezione. I messaggi di posta elettronica per i client di Regione Marche possono contenere informazioni confidenziali e con privilegi legali. Se non si è il destinatario specificato, non leggere, copiare, inoltrare o archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso di necessità ed urgenza, la risposta al presente messaggio di posta elettronica può essere visionata da persone estranee al destinatario.
> IMPORTANT NOTICE: This e-mail message is intended to be received only by persons entitled to receive the confidential information it may contain. E-mail messages to clients of Regione Marche may contain information that is confidential and legally privileged. Please do not read, copy, forward, or store this message unless you are an intended recipient of it. If you have received this message in error, please forward it to the sender and delete it completely from your computer system.
>
> --
> Questo messaggio stato analizzato da Libraesva ESG ed risultato non infetto.
> This message was scanned by Libraesva ESG and is believed to be clean.
>
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> [hidden email] mailing list -- To UNSUBSCRIBE and more, see
> https://urlsand.esvalabs.com/?u=https%3A%2F%2Fstat.ethz.ch%2Fmailman%2Flistinfo%2Fr-help&e=5a635173&h=06ff70f3&f=y&p=y
> PLEASE do read the posting guide https://urlsand.esvalabs.com/?u=http%3A%2F%2Fwww.R-project.org%2Fposting-guide.html&e=5a635173&h=e12f63e8&f=y&p=y
> and provide commented, minimal, self-contained, reproducible code.

--

Questo messaggio stato analizzato con Libraesva ESG ed risultato non infetto.

________________________________

AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere informazioni confidenziali, pertanto è destinato solo a persone autorizzate alla ricezione. I messaggi di posta elettronica per i client di Regione Marche possono contenere informazioni confidenziali e con privilegi legali. Se non si è il destinatario specificato, non leggere, copiare, inoltrare o archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso di necessità ed urgenza, la risposta al presente messaggio di posta elettronica può essere visionata da persone estranee al destinatario.
IMPORTANT NOTICE: This e-mail message is intended to be received only by persons entitled to receive the confidential information it may contain. E-mail messages to clients of Regione Marche may contain information that is confidential and legally privileged. Please do not read, copy, forward, or store this message unless you are an intended recipient of it. If you have received this message in error, please forward it to the sender and delete it completely from your computer system.

--
Questo messaggio stato analizzato da Libraesva ESG ed risultato non infetto.
This message was scanned by Libraesva ESG and is believed to be clean.

______________________________________________
[hidden email] 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.

Greg Minshall

Re: local maxima positions in a vector with duplicated values

Stefano,

i notice that my and Bill's (pretty much isomorphic) solutions give a
zero-length vector. i don't remember Bert's, but it's probably gives
similar results. your code could check for that result, and react
accordingly.

cheers, Greg

______________________________________________
[hidden email] 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.

Bill Dunlap-2

Re: local maxima positions in a vector with duplicated values

In reply to this post by Stefano Sofia

If you want to accept maxima at the ends of the series, append -Inf to
each end and subtract one from the result. Note that this will make
even a constant sequence have a local maximum at 1.

On Mon, Mar 29, 2021 at 6:52 AM Stefano Sofia
<[hidden email]> wrote:

>
> 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: [hidden email]
> ---Oo---------oO----------------------------------------
>
> ________________________________________
> Da: Bill Dunlap [[hidden email]]
> Inviato: venerdì 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
> <[hidden email]> 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: [hidden email]
> > ---Oo---------oO----------------------------------------
> >
> > ________________________________
> >
> > AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere informazioni confidenziali, pertanto è destinato solo a persone autorizzate alla ricezione. I messaggi di posta elettronica per i client di Regione Marche possono contenere informazioni confidenziali e con privilegi legali. Se non si è il destinatario specificato, non leggere, copiare, inoltrare o archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso di necessità ed urgenza, la risposta al presente messaggio di posta elettronica può essere visionata da persone estranee al destinatario.
> > IMPORTANT NOTICE: This e-mail message is intended to be received only by persons entitled to receive the confidential information it may contain. E-mail messages to clients of Regione Marche may contain information that is confidential and legally privileged. Please do not read, copy, forward, or store this message unless you are an intended recipient of it. If you have received this message in error, please forward it to the sender and delete it completely from your computer system.
> >
> > --
> > Questo messaggio stato analizzato da Libraesva ESG ed risultato non infetto.
> > This message was scanned by Libraesva ESG and is believed to be clean.
> >
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > [hidden email] mailing list -- To UNSUBSCRIBE and more, see
> > https://urlsand.esvalabs.com/?u=https%3A%2F%2Fstat.ethz.ch%2Fmailman%2Flistinfo%2Fr-help&e=5a635173&h=06ff70f3&f=y&p=y
> > PLEASE do read the posting guide https://urlsand.esvalabs.com/?u=http%3A%2F%2Fwww.R-project.org%2Fposting-guide.html&e=5a635173&h=e12f63e8&f=y&p=y
> > and provide commented, minimal, self-contained, reproducible code.
>
> --
>
> Questo messaggio stato analizzato con Libraesva ESG ed risultato non infetto.
>
>
> ________________________________
>
> AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere informazioni confidenziali, pertanto è destinato solo a persone autorizzate alla ricezione. I messaggi di posta elettronica per i client di Regione Marche possono contenere informazioni confidenziali e con privilegi legali. Se non si è il destinatario specificato, non leggere, copiare, inoltrare o archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso di necessità ed urgenza, la risposta al presente messaggio di posta elettronica può essere visionata da persone estranee al destinatario.
> IMPORTANT NOTICE: This e-mail message is intended to be received only by persons entitled to receive the confidential information it may contain. E-mail messages to clients of Regione Marche may contain information that is confidential and legally privileged. Please do not read, copy, forward, or store this message unless you are an intended recipient of it. If you have received this message in error, please forward it to the sender and delete it completely from your computer system.
>
> --
> Questo messaggio stato analizzato da Libraesva ESG ed risultato non infetto.
> This message was scanned by Libraesva ESG and is believed to be clean.
>

Stefano Sofia

Re: local maxima positions in a vector with duplicated values

Thank you Bill, your tip solved 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: [hidden email]
---Oo---------oO----------------------------------------

________________________________________
Da: Bill Dunlap [[hidden email]]
Inviato: lunedì 29 marzo 2021 17.22
A: Stefano Sofia
Cc: [hidden email]; [hidden email]; r-help mailing list
Oggetto: Re: [R] local maxima positions in a vector with duplicated values

If you want to accept maxima at the ends of the series, append -Inf to
each end and subtract one from the result. Note that this will make
even a constant sequence have a local maximum at 1.

On Mon, Mar 29, 2021 at 6:52 AM Stefano Sofia
<[hidden email]> wrote:

Bill Dunlap-2

Re: local maxima positions in a vector with duplicated values

Your original query included
> x <- c(1,0,0,0,2,2,3,4,0,1,1,0,5,5,5,0,1)
... I need 8 10 13.
Did you also want the 1's at the ends to count as local maxima,
so the result would be c(1,8,10,13,17)?
Or do you want the maxima at endpoints only if there are no others?

-BIll

On Mon, Mar 29, 2021 at 8:56 AM Stefano Sofia
<[hidden email]> wrote:

>
> Thank you Bill, your tip solved 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: [hidden email]
> ---Oo---------oO----------------------------------------
>
> ________________________________________
> Da: Bill Dunlap [[hidden email]]
> Inviato: lunedì 29 marzo 2021 17.22
> A: Stefano Sofia
> Cc: [hidden email]; [hidden email]; r-help mailing list
> Oggetto: Re: [R] local maxima positions in a vector with duplicated values
>
> If you want to accept maxima at the ends of the series, append -Inf to
> each end and subtract one from the result. Note that this will make
> even a constant sequence have a local maximum at 1.
>
> On Mon, Mar 29, 2021 at 6:52 AM Stefano Sofia
> <[hidden email]> wrote:
> >
> > 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: [hidden email]
> > ---Oo---------oO----------------------------------------
> >
> > ________________________________________
> > Da: Bill Dunlap [[hidden email]]
> > Inviato: venerdì 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
> > <[hidden email]> 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: [hidden email]
> > > ---Oo---------oO----------------------------------------
> > >
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Stefano Sofia

Re: local maxima positions in a vector with duplicated values

Maximum at the right endpoint is well accpted in both cases. If I am correst, I just append -Inf at the right end and then I apply what you wrote.

Thank you.

(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: [hidden email]
---Oo---------oO----------------------------------------

________________________________________
Da: Bill Dunlap [[hidden email]]
Inviato: lunedì 29 marzo 2021 18.03
A: Stefano Sofia
Cc: [hidden email]; [hidden email]; r-help mailing list
Oggetto: Re: [R] local maxima positions in a vector with duplicated values

Your original query included
> x <- c(1,0,0,0,2,2,3,4,0,1,1,0,5,5,5,0,1)
... I need 8 10 13.
Did you also want the 1's at the ends to count as local maxima,
so the result would be c(1,8,10,13,17)?
Or do you want the maxima at endpoints only if there are no others?

-BIll

On Mon, Mar 29, 2021 at 8:56 AM Stefano Sofia
<[hidden email]> wrote: