Eliminating peaks too close

Questions
1

Hi

I am working on a 1D (nice) data-set and trying to find its peaks. It picked 2 peaks (121th and 123th data points) due to obvious noises. I am only looking for a rough (not accurate, whichever of the two) location of the peak, but not like to get 2 peak locations. How could I:

  1. Set the FindPeaks parameter so it will only find 1 peak?
    or
  2. After get a list of peaks, how could I eliminate close ones among 5-10 peak resulted points?

Raw data and curve images are attached.

Many thanks.

Xiaxing Xiong

Example.txt (4.3 KB)

OSC-Signal.JPG
OSC-Signal.JPG390×154 5.02 KB

2

Welcome to Wolfram Community!
Please make sure you know the rules: https://wolfr.am/READ-1ST
Your post is too vague. Please describe your subject extensively providing code.

3

Please post the code you used to generate the plot. There are no negative values in Example.txt but the plot in OSC-Signal.jpg has negative values.

4

The following in my code:

DATA1 = -DATA[[400 ;; 599, All]];
ListPlot[DATA1[[All, 3]], 
 PlotRange -> {{100, 130}, {-0.0000024, -0.0000018
    }}]
FindPeaks[DATA1[[All, 3]], 5][[All, 1]]

The data I attached before is the DATA1
I am looking for peaks of this data set. The result it gives is {121,123}. The peaks found were too close. I just need one of them, whichever one. Could I change the parameter of the FindPeaks so that it will give only one peak?

Thanks

Xiaxing

5

Hi Rohit

Sorry the data is positive, and I am looking for the bottom position. So I multiply it with (-1) and looking for the peaks instead

Thanks for looking into my problem.

Xiaxing

6

Is there some underlying theoretical model? Or is the shape known but maybe not the coefficients such as a parabola? Or is it just data?

If “just data”, is there any idea of the measurement errors on each sample point?

7

Without a better understanding of your requirements, I think something like this might work:

data = {100, 3, 2, 103, 102, 5, 4, 2, 105, 104, 103, 3};

findPeaks[ data_List, tolerance_List] := Module[
   {
    peaks = FindPeaks[data]
    , lastPeak = {-Infinity, -Infinity}
    , forward
    , reverse
    },
   forward = Map[
     With[
       {
        retVal = If[
          And[
           First[#1] -  First[lastPeak] <= tolerance[[1]],
           Last[#1] - Last[lastPeak] <= tolerance[[2]]
           ]
          ,
           Nothing
          ,
          #1
          ]
        }
       ,
       lastPeak = #1
       ] &
     ,
     peaks
     ];
   
   
   reverse = Map[
     With[
       {
        retVal = If[
          And[
           First[#1] -  First[lastPeak] <= tolerance[[1]],
           Last[#1] - Last[lastPeak] <= tolerance[[2]]
           ]
          ,
           Nothing
          ,
          #1
          ]
        }
       ,
       lastPeak = #1
       ] &
     ,
     Reverse[forward]
     ];
   
   Reverse[reverse]
   
   ];

findPeaks[data, {3, 3}]
8

The data I attached before is the DATA1

Example.txt only has 2 columns so, it cannot be DATA1 because this would not work

ListPlot[DATA1[[All, 3]], ...
9

A simple peak finder

findPeaks[list_] := (list // BlockMap[(#[[1]] < #[[2]] > #[[3]] &), #, 3, 1] & // Position[True]) + 1

On Mike’s sample data

peaks = findPeaks@data;
values = Extract[data, peaks];

ListPlot[{data, Transpose[{Flatten@peaks, values}]}, 
 PlotStyle -> {Automatic, Red}]

9917plot.png
9917plot.png450×282 2.44 KB

10

Rohit:

Thanks again for teaching me a new trick. I can see how BlockMap[] can be very useful.

11

Dear Friends.

Thank many of you for your help. After a night of think, I got myself the following code to solve some close bottom min data set and eliminated the near by repeat one. Still，

Many thanks for you tips and inspirations!

Xiaxing

BOTTS
NUMB = Dimensions[BOTTS][[1]]
For[i = NUMB - 1, i > 0, i--, 
 BOTTS = If[BOTTS[[i + 1]] - BOTTS[[i]] < 5, Drop[BOTTS, {i}], BOTTS];]
BOTTS

The BOTTS before the code gives

{2, 262, 520, 522, 775, 1028, 1274, 1517, 1757, 1993, 2225, 2455, \
2684, 2905, 3125, 3344, 3558, 3560, 3769, 3978}

The BOTTS after the code gives

{2, 262, 522, 775, 1028, 1274, 1517, 1757, 1993, 2225, 2455, 2684, \
2905, 3125, 3344, 3560, 3769, 3978}

The code eliminated of the the nearby peak@520，@3558