How to plot a 1 x 1 struct with 175 fields in Matlab

I converted my .lvm file into matlab using the function by M. A. Hopcroft ( LVM File Import ).

Now, my workspace has ans as a 1 x 1 struct. The 1 x 1 struct has 175 fields, with 5 extra fields as text*. Thus a total of 180 fields.

I need help plotting my data. In my 1 x 1 struct, I have Segment1 to Segment175. In each, there is a another subfolder called data, in which there are 10000 rows and 2 columns of values. How do I plot ans.Segment1.data, ans.Segment2.data, ans.Segment3.data, ... ,ans.Segment175.data into ONE graph?

*Please let me know if the 5 text fields for each segment data confuses matlab in some kind of way.

[Christopher Wallace]

Can you provide sample data?

[Michael Molyneaux-Francis]

I have provided data for only 2 segments (since they are quite large). Time is the first column and amplitude is the second column. You can see that each segment spans 1 second.

ans.Segment1.data

0 0.00034

0.0001 0.000176

0.0002 0.000176

0.0003 0.000176

0.0004 0.00034

... ...

0.9995 0.000505

0.9996 0.000176

0.9997 0.00034

0.9998 0.00034

0.9999 0.000176

ans.Segment2.data

1 0.000176

1.0001 0.000176

1.0002 0.000176

1.0003 0.000669

1.0004 0.00034

1.0005 0.00034

... ...

1.9995 0.00034

1.9996 0.000176

1.9997 0.000176

1.9998 0.00034

1.9999 1.13E-05

Answer 1

[Stephen23]

Unfortunately putting numbers into fieldnames like that makes it all rather tricky, because putting (meta)-data into the fieldnames makes them awkward to handle. The data should have been stored in a non-scalar structure, because indexing is much simpler and more efficient.

As Adam Danz wrote, using ans is a bad idea. Better call your structure s or something more explanatory of its contents. Then you could use dynamic fieldnames like this:

s.Segment1.data = [0,0.00034;0.0001,0.000176;0.0002,0.000176;0.0003,0.000176;0.0004,0.00034;0.9995,0.000505];
s.Segment2.data = [1,0.000176;1.0001,0.000176;1.0002,0.000176;1.0003,0.000669;1.0004,0.00034;1.0005,0.00034];
... all the other fields
s.otherfield = 'blah';
for k = 1:175
    fnm = sprintf('Segment%d',k);
    plot(s.(fnm).data(:,1),s.(fnm).data(:,2))
    hold on
end

Or a a bit neater and clearer would be to use a temporary variable:

for k = 1:175
    fnm = sprintf('Segment%d',k);
    tmp = s.(fnm).data;
    plot(tmp(:,1),tmp(:,2))
    hold on
end

[Michael Molyneaux-Francis]

Thank you Stephen. I'm now experiencing a problem with the axes. It seems that my axes are reversed. The max of the x axis should be 174.9 and the max of the y axis should be 10,000.

I also tried doing view([90 -90]), which didn't work as well. The graph should look like a waveform.

What am I doing wrong?

[Stephen23]

@Michael Molyneaux-Francis: you will need to provide the x and y values as separate inputs to plot, like this:

plot(s.(fnm).data(:,1),s.(fnm).data(:,2))

[Michael Molyneaux-Francis]

That worked! Thank you.

Answer 2

[Adam Danz]

This should get you halfway there. The other half depends on how you're plotting the data which isn't described.

Instead of 'ans', I'll call your structure 's' (never use 'ans' as a variable name).

sArray = struct2array(s); 
sMat = [sArray.data];

If you want all of your data organized vertically into two columns,

cell2mat({sArray.data}');

Use reshape() if you need your data organized differently.

If you're plotting in a loop,

sCell = {sArray.data}; 
for i = 1:length(sCell)
   ...sCell{i}...
end

[Michael Molyneaux-Francis]

Adam,

Thank you for your input. Your advice did not work for me. I have attached a screenshot image of the error readings. Do you happen to know if I'm missing a toolbox of some sort?

[Stephen23]

Note that struct2array is not a MATLAB function (it was used in some toolbox several years ago).

Note that

cell2mat({sArray.data}');

would be simpler as:

vertcat(sArray.data)

[Adam Danz]

Good catch. Instead of my code above, here's the replacement without using struct2array().

sCell = struct2cell(s); 
sArray = [sCell{:}];

* Not tested.