How to plot graph using data from a text file?

Attached is the sound.txt file and questions.

How do we plot a graph with said x and y values? i have tried this but to no success.

filename='sound.txt';
fid= fopen(filename,'r');
header = fscanf(fid,'%s',[1 1]);
headerx= fscanf(fid,'%f',[1 8]);
headery=[];
data=[];
for k= 1:24
   headery= [headery; fscanf(fid,'%f',[1 1])];
   data = [data; fscanf(fid,'%f',[1 8])];
end

mesh(headerx,headery,data)

Help please :)

[Geoff Hayes]

bala - what is wrong with the plot from mesh? Is that not what you are expecting?

[Star Strider]

Use readmatrix to import the file. (If you do not have readmatrix, then textscan would probably be your next most appropriate alternative.) You then have to remove the top row and the first column and save them separately (those will be your x and y coordinates respectively), and plot the rest of the matrix.

This is a MATLAB programming assignment, so it would not be appropriate to give specific help on the rest of it.

[bala balu]

I was looking to plot a graph with the said x and y coordinates as the scale. I mistakenly did a mesh graph. It’s supposed to be a normal 2D graph with the said x and y coordinates. I’m very lost on how to plot out a graph with the said x and y scales. I did the textscan but how do you use the plot function with those x and y coordinates. I’m very new to Matlab :D

[bala balu]

I don’t understand what you mean by saving the x and y coordinates separately, do you mean save it to another text file? How do I use the plot function based on your suggestion?

[Star Strider]

I believe the assignment wants you to do a contour plot. The coding for that is similar to a mesh plot.

Save the x and y values as vectors in your workspace. Save the rest of the data as a matrix.

[bala balu]

Do you means using like X=[-10:5:25] when you meant saving it as a vector? And can you please clarify what you meant by saving the rest as a matrics? How do you accomplish that?

[Star Strider]

‘Do you means using like X=[-10:5:25] when you meant saving it as a vector?’

Yes. Although you need to read it (and the y-vector) from the file.

‘And can you please clarify what you meant by saving the rest as a matrics? How do you accomplish that?’

The entire array will be imported as a matrix. For the rest, see the documentation section on Matrix Indexing (link).

[bala balu]

I have successfully completed my assignment. Thanks for all the help!

Answer 1

[KSSV]

Replace y/x in the text file with NaN.

A = load('sound.txt') ; 

x = A(1,2:end) ; 
y = A(2:end,1) ; 
Z = A(2:end,2:end) ; 

figure
surf(x,y,Z) 
figure
pcolor(x,y,Z)
figure
contour(x,y,Z)

[bala balu]

Okay I shall try this and see if I have any luck, will update here ASAP.

[bala balu]

Thank you, i managed to produce a graph with this.

[Peter Arandorenko]

Can you show us how it looks like?