Saving a Structured Array (containing plot parameters) to a mat file

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Jason
Jason 2024-6-24
评论： Jason 2024-6-24
Hi, Im trying to save plot data by using a structured arra
ax=app.UIAxes;
ax.Children;
h1 = findall(ax, 'type', 'line'); % Line objects
nlines=numel(h1);
Assign the desired plot parameters to a struct "S"
for i=1:nlines
thisLine=h1(i);
S(i).Xdata=thisLine.XData; S(i).Ydata=thisLine.YData;
S(i).Colour=thisLine.Color;
S(i).LineStyle=thisLine.LineStyle;
S(i).LineWidth=thisLine.LineWidth;
S(i).DName=thisLine.DisplayName;
end
Save to a .MAT file
try
[file,folder]=uiputfile({'*.mat','Matlab Files'},'Save Data',app.startfolder);
catch
[file,folder]=uiputfile({'*.mat','Matlab Files'},'Save Data','C:\');
end
app.startfolder=folder;
savepath=fullfile(folder,file);
save(savepath,"-struct",'S')
But I keep getting this error:
Error using save
The argument to -STRUCT must be the name of a scalar structure variable.
I have checked the class of S and the fieldnames contained within it:
fields = fieldnames(S)
class(S)
fields =
6×1 cell array
{'Xdata' }
{'Ydata' }
{'Colour' }
{'LineStyle'}
{'LineWidth'}
{'DName' }
ans =
'struct'
Thanks for any help

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采纳的回答

Stephen23
Stephen23 2024-6-24
编辑：Stephen23 2024-6-24
Explanation: your structure is not scalar: it has nlines elements. The -struct option only works with scalar structures.
Error using save
The argument to -STRUCT must be the name of a scalar structure variable.
% ^^^^^^
Solutions:
  • either get rid of the -struct option, or
  • create a scalar structure (by making the fields arrays, not the structure).
Tip: always LOAD into an output variable!
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Steven Lord
Steven Lord 2024-6-24
Ran in:
Since several of the properties you're trying to store in the struct are non-scalar, it won't work as you wrote it. But you could have the fields of the scalar struct contain cell arrays, where each cell in the array can have data of different sizes depending on the properties of the specific line you're trying to store inside it.
h = plot(1:10, 1:10, 'r-', 1:7, 10:-1:4, 'k:');
for k = 1:numel(h)
S.XData{k} = h(k).XData;
S.YData{k} = h(k).YData;
end
disp(S)
XData: {[1 2 3 4 5 6 7 8 9 10] [1 2 3 4 5 6 7]} YData: {[1 2 3 4 5 6 7 8 9 10] [10 9 8 7 6 5 4]}
isscalar(S) % yes
ans = logical
1
isstruct(S) % also yes
ans = logical
1
cd(tempdir)
save('mydata.mat', '-struct', 'S')
whos -file mydata.mat
Name Size Bytes Class Attributes XData 1x2 344 cell YData 1x2 344 cell
P = load('mydata.mat')
P = struct with fields:
XData: {[1 2 3 4 5 6 7 8 9 10] [1 2 3 4 5 6 7]} YData: {[1 2 3 4 5 6 7 8 9 10] [10 9 8 7 6 5 4]}
isequal(P, S)
ans = logical
1

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