Extracting data from multiple structures in a .mat file

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John Doe
John Doe 2019-6-13
评论： John Doe 2019-6-13
Hello,
I have some data which is in nested structures names an example structure is below.
Signal_00.y_values.values
I want to extract this data using a foor loop and place it all in m x n array when m is the original structure, and n the number of points. Here's where I got to:
sigName = {'Signal_00';'Signal_01';'Signal_02';'Signal_03'...}
for k = 1:24
tData(k,:) = sigName(k).y_values.values
end
The error I recieve in command window when I try to open the data is:
>> sNames(1).y_values.values
Dot indexing is not supported for variables of this type.
What is the correct way to generate a structure path which can be used in the for loop?
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Stephen23
Stephen23 2019-6-13
编辑：Stephen23 2019-6-13
@KSSV: "First of all: does this code work:"
sigName = {'Signal_00';'Signal_01';'Signal_02';'Signal_03'...}
for k = 1:24
tData(k,:) = sigName(k).y_values.values
end
if sigName is a cell array of character vectors, then sigName(k) will return a scalar cell array... and what do you expect the dot notation to achieve with a scalar cell array?

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Stephen23
Stephen23 2019-6-13
编辑：Stephen23 2019-6-13
Do NOT load directly in the workspace.
If you do that, then you will force yourself into writing slow, complex, buggy code by trying to access the variable names dynamically. Read this to know why this is a bad approach to writing code:
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
The solution is very simple: always load into an output variable (which is a scalar structure):
S = load(...)
The variables in the .mat file are the fields of that scalar structure. You can trivially and efficiently iterate over the fields of that structure:
F = fieldnames(S);
for k = 1:numel(F)
S.(F{k}).y_values.values
end
https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html
Note that if you have multiple .mat files then your code would also be much simpler if each .mat contained variables with exactly the same names. Having lots of numbered variables is a sign that you are doing something wrong (i.e. you should be using indexing).
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Stephen23
Stephen23 2019-6-13
F is a cell array of fieldnames, you need to use idexing, e.g.
S.(F{k}).y_values.values
% ^^^ do not forget the index!

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