Creating a single .mat file by combining several .mat files

Hi,

I have x number of .mat files that are structured in the same way.

Each .mat file has a variable named mydata.

I want to generate a fresh.mat file, such that the variable mydata of each file is stored in the name of its parent .mat file.

For example:

1.mat contains mydata

2.mat contains mydata

...

x.mat contains mydata

The new file, fresh.mat must contain variables named as 1 2 3 .. x

How can I do this ?

Answer 1

[David Szwer]

This can be done with structures. Here's a demonstration - only the middle cell is the code you actually need.

%% Set up the demonstration.
mydata = "1"; save("mat1.mat", "mydata");
mydata = "2"; save("mat2.mat", "mydata");
mydata = "3"; save("mat3.mat", "mydata");
mydata = "Thew, thew, thew!"; save("matthew.mat", "mydata");
% Note that if your files are really just called "1.mat" etc., this won't work; no
% Matlab variable can have a name that starts with a number.

%% The solution
% List your file names here, without path or extension.
filenames = ["mat1" "mat2" "mat3" "matthew"];
for filename = filenames
  % The command:
  % S = load(filename + ".mat");
  % creates a structure "S" whose fields are the variables in the .mat file.  For
  % you, that's just "mydata", so you would end up with a structure "S.mydata".
  % Instead, lets put it in a sub-structure named after the file name.
  %
  % Add the full path to the load() command if you need to.
  structFromMatFile.(filename) = load(filename + ".mat");

  % Remove your data from the field called "mydata", and put it directly in the
  % field named after the file name.
  structFromMatFile.(filename) = structFromMatFile.(filename).mydata;
end

% The save() function has an option that saves every field in a structure into a
% .mat file, as separate variables named after the field.
save("fresh.mat", "-struct","structFromMatFile")

%% Show that all the data were saved.
clear("variables")

load("fresh.mat")
whos

  Name         Size            Bytes  Class     Attributes

  mat1         1x1               150  string              
  mat2         1x1               150  string              
  mat3         1x1               150  string              
  matthew      1x1               170  string              

Relevant help pages are:

load > Load List of Variables into Structure Array: https://uk.mathworks.com/help/releases/R2023a/matlab/ref/load.html#btm3ohm-1

save > Save Structure Fields as Individual Variables: https://uk.mathworks.com/help/releases/R2023a/matlab/ref/save.html#mw_f7e7216d-94c3-47ff-a2c6-b68edf25ffa8

Generate Field Names from Variables: https://www.mathworks.com/help/releases/R2023a/matlab/matlab_prog/generate-field-names-from-variables.html