Issues with findpeaks()

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)

[Joshua Walters]

The CSV file is here

Answer 1

[ME]

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!

[Star Strider]

Right.

Try this:

findpeaks(col2)

or:

findpeaks(col2,col1)

Use the name-value pair arguments as necessary to get the desired result.

[Joshua Walters]

So I tried doing findpeaks(col2,col1) and I got a graph that had was very odd looking to me.

When I don't put in the findpeaks(col2,col1) that the graph is the first image (notice the x-axis).

When I do it's the 2nd image, the x-axis looks very different and I do not know why.

I've also tried using [len,pks]=findpeaks(col2,col1) and then plotting those.

It still looks strange and I really don't understand what's going on.

clear all;
clc;

%ME451 Lab 2 Signoff 3
data=importdata("Light-Lab2.csv");
col1 = data(:,1);
col2 = data(:,2);
plot(col1,col2)
grid on, grid minor
title('Lab 2 signoff 3 light data')
xlabel("Time")
ylabel("voltage")
%[len,pks]=findpeaks(col2,col1) %using this for a plot
%plot(len,pks)    

%findpeaks(col2,col1)           %from previous suggestion             
% xlabel("Time")
% ylabel("voltage")
% title("Peaks")
%findpeaks(col2,'MinPeakDistance',2); %no lower arrows & no 2nd plot

[Joshua Walters]

Here's the strange graph I get with the [len,pks] plot

[Joshua Walters]

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]

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?