Matlab accessing structures

Question

I am trying to access data that are stored in structures in matlab. Having many files I am trying to make the process automatic, however I have a problem in accessing the struct using the structure name (given that it is a string). Also, storing the structure in a variable (as shown below) does not work either, because matlab attaches the whole structure to the variable. Does anybody have an idea on how to do this?

%Initialize variables
Data_Struct = load(dirData(1).name);
file_id = fieldnames(Data_Struct);
data = Data_Struct.Trajectories;

Here a screenshot of the struct containing the data

Can you upload one test case, or the screenshot of how the data is organized in the struct? — amahmud
– amahmud, Commented Dec 3, 2018 at 9:44
What's inside the Trajectories? If another struct called 'Labeled', then what's inside of this? — amahmud
– amahmud, Commented Dec 3, 2018 at 10:02
Yes inside Trajectories, there is another structure called Labelled, and then a matrix of data — Simon
– Simon, Commented Dec 3, 2018 at 10:18
data = Data_Struct.Trajectories.Labelled.(name of the data matrix) This will provide the data matrix as a variable. — amahmud
– amahmud, Commented Dec 3, 2018 at 10:29

amahmud · Accepted Answer · 2018-12-03 11:00:14Z

2

The file name is changing every time so you need to get the it correctly when loading a new struct.

Data_Struct = load(dirData(1).name);

After this line,

name = fieldnames(Data_Struct);

This will give you the unique name of your file. Finally,

data = Data_Struct.(name{1}).Trajectories.Labelled.(name of the data matrix)

answered Dec 3, 2018 at 11:00

amahmud

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l.fabbrini · Accepted Answer · 2018-12-03 11:02:44Z

The trick here is to exploit the fact that you can acces to a structure field by its name string as:

name = 'Trajectories'
value = Data_Struct.(name)

So, in your case, to get unrolled values as Cell Array you can use:

%%Little example copying some of your structure
Data_Struct.Trajectories.Labelled = zeros(10);
Data_Struct.Analog = zeros(10);
Data_Struct.FrameRate = 300;

[UnrolledCell] = getUnrolledVal(Data_Struct,[]);
display(UnrolledCell)

UnrolledCell =

3×2 cell array

'Labelled'     [10×10 double]
'FrameRate'    [         300]
'Analog'       [10×10 double]

Here the getUnrolledVal function is simply:

function [UnrolledCell] = getUnrolledVal(struct_in,UnrolledCell)
fields_list = fieldnames(struct_in);
for i=1:length(fields_list)
    field = fields_list{i};
    if isstruct(struct_in.(field))
        UnrolledCell = getUnrolledVal(struct_in.(field),UnrolledCell);
    else
        UnrolledCell = [UnrolledCell; {field} {struct_in.(field)}];
    end
end

end

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