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Issues with findpeaks()

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Joshua Walters
Joshua Walters on 28 Apr 2020
Commented: ME on 28 Apr 2020
I'm having issues with using findpeaks() for lab data.
I have my script calling a csv file with 2 columbs of data.
As you can see from my script I can get the data to plot easily, however when I insert findpeaks(col1,col2) or findpeaks(data) I get an error message I don't understand.
The error I get is as follows:
----
Error using findpeaks
Expected Y to be a vector.
Error in findpeaks>parse_inputs (line 199)
validateattributes(Yin,{'double','single'},{'nonempty','real','vector'},...
Error in findpeaks (line 136)
= parse_inputs(isInMATLAB,Yin,varargin{:});
---
Can anyone please explaene to me why this isn't working.
clear all;
clc;
%Lab 2 Signoff 3
data=importdata("Light-Lab2.csv");
col1 = data(:,1);
col2 = data(:,2);
plot(col1,col2)
grid on, grid minor
title('lab2 data')
xlabel("Time")
ylabel("voltage")
findpeaks(data)
%findpeaks(col1,col2)

  1 Comment

Joshua Walters
Joshua Walters on 28 Apr 2020
The CSV file is here

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Accepted Answer

ME
ME on 28 Apr 2020
I must stress that I am not sure and I don't have acces to the Signal Processing Toolbox to check. However, have you tried reversing the order of col1, col2 in your find peaks command?
I think that command is asking it to output the x-axis locations of the peaks in your y-axis data. This would be done as findpeaks(data,x). Therefore your x-data needs to be the second input argument and at present I think they are the wrong way around.
I think the issue when you try findpeaks(data) is that you aren't feeding in a vector (1xN) but rather an array (2xN).
I hope that helps!

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Joshua Walters
Joshua Walters on 28 Apr 2020
Here's the strange graph I get with the [len,pks] plot
Joshua Walters
Joshua Walters on 28 Apr 2020
Update,
This ended up getting me, I think, what I needed:
clear all;
clc;
%ME451 Lab 2 Signoff 3
data=importdata("Light-Lab2.csv");
col1 = data(:,1)/1000;
col2 = data(:,2);
plot(col1,col2)
grid on, grid minor, hold on
title('Lab 2 signoff 3 light data')
xlabel("Time")
ylabel("voltage")
[pks,len]=findpeaks(col2,col1,'MinPeakHeight',1.5); %using this for a plot
plot(len,pks,'r*')
grid on, grid minor
%findpeaks(col2,col1) %from previous suggestion
xlabel("Time")
ylabel("voltage")
title("[Insert swear word here]")
%findpeaks(col2,'MinPeakDistance',2); %no lower arrows & no 2nd plot
time_s=length(col1)/32.66;
avg_freq=1/time_s;
fprintf('Average frequency = %6.2f Hz',avg_freq)
Thanks for your help :)
ME
ME on 28 Apr 2020
No problem, apologies I couldn’t be more help. Without access to the toolbox I couldn’t test anything out.
Anyway, if this helped you would you possibly consider accepting my answer?

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