MATLAB: Loading and storing specific field of many different file names of a struct

file namesfor loopsstruct

Hi everyone, I have a set of 100 readings from a test rig, all are multilevel struct .mat files. I am trying to group a specific field (which is common within all the files) into a single row matrix (100,:). So from the help of the Mathworks community i was able to load all the 100 files into one struct, but my real objective is to get a specific field,

folder_name=uigetdir(); 
filenameExtension='.mat';
TempMatrix=cell(100,1);
for n=1:100
    filename=[folder_name,'\exp_0',int2str(n),filenameExtension];
    TempMatrix{n,:}=load(filename);
    
end

all the files i want to load are named as exp_01.mat, exp_02.mat…….exp_0100.mat

the only way to accest the file I want is like this:

example for exp_02:

FinalMatrix=[TempMatrix(2).data.exp_02.Y(3).Data];

so u see i need to change the file name each time to get the answer. But how do i get it in a for loop to store all the 100 files target field(Y(3)) into a single array matrix for ease of access.

Any help/advice would be realy appreciated. Thank you.

iv attached few example files.

Best Answer

When using structures you can use variables and expressions to access fields using () . For instance lets say you had the following.

x.b1=1;
x.b2=2;
y = zeros(2,1)
% You can access the fields in a loop by using ()
for i=1:2
    y(i)=x.(['b' num2str(i)]);
    
end

So assuming I'm understanding your problem correctly you could do:

filename = ['exp_0',int2str(n)];
FinalMatrix=[TempMatrix(2).data.(filename).Data];

Related Solutions

MATLAB: How to load saved workspace in a custom named variable

The efficient approach is to use indexing (rather than anti-pattern dynamic variable names):

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

It is easy to import the file data into one cell array or one structure, e.g. the same one that dir returns:

D = 'absolute or relative path to the folder where the files are saved';
S = dir(fullfile(D,'*mat'));
for k = 1:numel(S)
    F = fullfile(D,S(k).name);
    S(k).data = load(F);
end

and then you can simply access the data from every file using basic and very efficient indexing, e.g. the third file:

S(3).name
S(3).data

If all of your .mat files contain variables with the same names (which is good data design) then you can also un-nest them by concatenating the data structures them into one non-scalar structure, e.g.:

out = [S.data]
out(3).someVariable
out(3).otherThing

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

MATLAB: Execute a loop with diffrent name

You could do this in two loops using sprintf , something like this:

for k1 = [50,86]
    for k2 = 1:100
        file_name = sprintf('data%u_%u.mat',k1,k2);
        load(file_name)
    end
end

Currently your code will completely replace the data from the previous loop, as on every iteration it assigns new data to the variable A. If you wish to avoid this, then you need to use some indexing to store all of the data, or consider using a structure and dynamic field names to store the load data directly:

A = struct([]);
for k1 = [50,86]
    for k2 = 1:100
        file_name = sprintf('data%u_%u.mat',k1,k2);
        A(k2).(sprintf('data%u',k1)) = load(file_name);
    end
end

Structures have lots of other useful tools and features to make working with your data easy.

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