Error using findpeaks Expected Y to be one of these types: double, single Instead its type was table.

Hi,

I am trying to read a file and find its peak. But the findpeak function keeps throwing errors. Please help. I am new to matlab.

%clear,clc
readtable('KD.xlsx');
x=qw(:,1);
y=qw(:,2);
%y=data(:,2');
Peaks=findpeaks(ans);
[pks,locs] = findpeaks(KD);
plot(x,y,y(locs),pks,'or')
xlabel('Xvalue')
ylabel('Peak')
axis tight

error message:

Error using findpeaks

Expected Y to be one of these types:

double, single

Instead its type was table.

Error in findpeaks>parse_inputs (line 199)

validateattributes(Yin,{'double','single'},{'nonempty','real','vector'},...

Error in findpeaks (line 136)

= parse_inputs(isInMATLAB,Yin,varargin{:});

Error in Untitled (line 6)

Peaks=findpeaks(ans);

[Walter Roberson]

You have a clear at the top of your code. Where are you expecting the array qw to be pulled out of?

Peaks=findpeaks(ans);

I recommend against relying on the value of ans in programming. Someone (you, later in time) should not have to know that inserting additional statements that do not modify existing variables could end up changing the meaning of the code because they happen to change ans.

[Venkatakrishnan Rengarajan]

My bad. I have my array imported in the name qw.

Answer 1

[Cris LaPierre]

Best to use variable you define rather than ans.

The function readtable returns a table. Each column of a table is, in turn, a variable. So a table is made up of variables.

The input for findpeaks must be a variable, but you are passing in the entire table. The error will be fixed if you can instead pass in a variable.

See this page for how to access data in a table. Any of the syntaxes that return an array are what you need. If you know the variable name, the simplest is to use dot notation.

Peaks=findpeaks(Tname.Varname);

[Venkatakrishnan Rengarajan]

So it should be findpeaks(ans.y) or findpeaks(y)? I tried both. It was still showing the same error.

[Cris LaPierre]

You shouldn't be using ans. Assign the output of readtable to a variable you create.

I also don't know what your variable names are in your table, so I can't comment on that either. Perhaps you can attach your spreadsheet to your post. Use the paperclip icon.

[Venkatakrishnan Rengarajan]

Here is my table. I will try assiging the variables. It did not work. However, I will try again. Obviously, I am doing something wrong.

[Cris LaPierre]

If you are having trouble assigning variables, you should really take the time to complete MATLAB Onramp. Creating variables and assigning them values is a fundamental skill you need to understand.

Simplifying your code, here is how i would load and plot the data.

data = readtable('KD.xlsx');
x=data.Var1;
y=data.Var2;
[pks,locs] = findpeaks(y);
plot(x,y,x(locs),pks,'or')
xlabel('Xvalue')
ylabel('Peak')

[Venkatakrishnan Rengarajan]

I understand the variable assignment. However, the problem still persists. I copied the modified code of yours and ran again. It did not help. I tried many iterations.

Peak

Error using findpeaks

Too many output arguments.

Error in Peak (line 4)

[pks,locs] = findpeaks(y);

This is the error now. Maybe I should access the signal acquistion toolbox and put that in the path. Thanks a lot for taking your time to help me. I really appreciate it.

[Walter Roberson]

What shows up for

which -all findpeaks

[Venkatakrishnan Rengarajan]

I just realized that, before starting this problem, I downloaded a set of functions from a university website. It had findpeaks command in it. The input in that command was different compared to the default "findpeak" command in the signal processing toolbox. After I deleted the my downloaded package (i just changed the file path, tbh), it worked perfectly.

Thanks for all the comments and help. I really appreciate it.