For loop to store one matrix from multiple files to a structure

Hello everyone,

I am trying to create a for-loop to go through multiple files store a single matrix from each file into a structure.

The code I am currently using allows me to pull the necessary matrix but will not store them all into one structure

cd 'C:\Users\Document\Data'
a = dir('*.mat');
b = 1;
filename = a(b).name;
for i=1:size(a,1)
    tempdata = importdata(filename);
    all_new = tempdata.results;
        
    b = b+1;
    
end

By the end, I am hoping to have a structure that contains the matrix "tempdata.results" from all the files in 'C:\Users\Document\Data'.

Thank you!

Answer 1

[Walter Roberson]

projectdir = 'C:\Users\Document\Data';
dinfo = dir(fullfile(projectdir, '*.mat'));
filenames = fullfile( {dinfo.folder}, {dinfo.name});
numfiles = length(filenames);

all_new(numfiles,1) = struct('results',[]);  %pre-allocate

for K = 1 : numfiles
    tempdata = load(filenames{K}, 'results');  %should contain only results
    all_new(K) = tempdata;
end

It would probably be more common to use a cell array than a struct array, but you specifically asked for a structure.

In the case where the arrays are all the same size, you can often gain performance advantages by using a multidimensional array of data instead of a cell array or struct array.

[John Kim]

Thank you very much!

It worked perfectly.

Could you elaborate on what you mean by multidimensional array?

[Stephen23]

"Could you elaborate on what you mean by multidimensional array?"

https://www.mathworks.com/help/matlab/math/multidimensional-arrays.html

Answer 2

[Stephen23]

P = 'C:\Users\Document\Data';
S = dir(fullfile(P,'*.mat'));
for k = 1:numel(S)
    F = fullfile(S(k).folder,S(k).name);
    S(k).data = load(F);
end
out = [S.data] % one structure

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

https://www.mathworks.com/matlabcentral/answers/1656435-tutorial-comma-separated-lists-and-how-to-use-them

[John Kim]

Thank you for the suggestion!