Re: [R] finding peaks in a simple dataset with R

From: Marc Kirchner <marc.kirchner_at_iwr.uni-heidelberg.de>
Date: Thu 24 Nov 2005 - 01:33:28 EST

>
> I wonder if we shouldn't polish that a bit and add to R's
> standard 'utils' package.
>

Hm, I figured out there are (at least) two versions out there, one being the "original" idea and a modification.

versus

Comparison shows
> peaks(c(1,4,1,1,6,1,5,1,1),3)

[1] TRUE FALSE FALSE TRUE FALSE TRUE FALSE which is a logical vector for elements 2:N-1 and

> peaks2(c(1,4,1,1,6,1,5,1,1),3)

[1] FALSE TRUE FALSE FALSE TRUE FALSE TRUE which is a logical vector for elements 1:N-2.

As I would expect to "lose" (span-1)/2 elements on each side of the vector, to me the 2001 version feels more natural.

Also, both "suffer" from being non-deterministic in the multiple-maxima-case (the two 4s here)

> peaks(c(1,4,4,1,6,1,5,1,1),3)

[1] FALSE TRUE FALSE TRUE FALSE TRUE FALSE
> peaks(c(1,4,4,1,6,1,5,1,1),3)

[1] TRUE TRUE FALSE TRUE FALSE TRUE FALSE
> peaks(c(1,4,4,1,6,1,5,1,1),3)

[1] FALSE FALSE FALSE TRUE FALSE TRUE FALSE
> peaks(c(1,4,4,1,6,1,5,1,1),3)

[1] FALSE TRUE FALSE TRUE FALSE TRUE FALSE which also persits for span > 3 (without the 6 then, of course):

> peaks(c(1,4,4,1,1,1,5,1,1),5)

[1] TRUE FALSE FALSE FALSE TRUE
> peaks(c(1,4,4,1,1,1,5,1,1),5)

[1] FALSE FALSE FALSE FALSE TRUE
> peaks(c(1,4,4,1,1,1,5,1,1),5)

[1] TRUE FALSE FALSE FALSE TRUE This could (should?) be fixed by modifying the call to max.col()

        result <- max.col(z, "first") == 1 + span %/% 2;

Just my two cents,
Marc

-- 
========================================================
Dipl. Inform. Med. Marc Kirchner
Interdisciplinary Centre for Scientific Computing (IWR)
Multidimensional Image Processing
INF 368
University of Heidelberg
D-69120 Heidelberg
Tel: ++49-6221-54 87 97
Fax: ++49-6221-54 88 50
marc.kirchner@iwr.uni-heidelberg.de


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Received on Thu Nov 24 01:54:18 2005

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