Load Multiple .mat Files to Matlab workspace

Question

I'm trying to load several .mat files to the workspace. However, they seem to overwrite each other. Instead, I want them to append. I am aware that I can do something like:

S=load(file1)
R=load(file2)

etc.

and then append the variables manually.

But there's a ton of variables, and making an append statement for each one is extremely undesirable (though possible as a last resort). Is there some way for me to load .mat files to the workspace (by using the load() command without assignment) and have them append?

By "they seem to overwrite each other" do you mean there is the same variable name in those .mat files? If that is the case there is nothing that can be done, except you load files one-by-one and then rename the variable that is shared on both files and then load the next file. — TJ1, Jul 16 '12 at 07:04

score 2 · Accepted Answer · answered Jul 16 '12 at 05:08

2

Its not entirely clear what you mean by "append" but here's a way to get the data loaded into a format that should be easy to deal with:

file_list = {'file1';'file2';...};
for file = file_list'
    loaded.(char(file)) = load(file);
end

This makes use of dynamic field references to load the contents of each file in the list into its own field of the loaded structure. You can iterate over the fields and manipulate the data however you'd like from here.

answered Jul 16 '12 at 05:08

tmpearce

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This is not quite the answer I wanted but probably the next best thing, given that what I want can't be done. I'll go ahead and accept it. – CHP Jul 17 '12 at 08:08
Once everything has been loaded, you can use `fieldnames` to figure out all the different variables you have loaded into the structure. You can then `eval` to get them into the workspace (instead of just in the structure), "appending" (however you define it) as needed. – tmpearce Jul 17 '12 at 13:46

score 2 · Answer 2 · answered Oct 09 '12 at 14:19

It sounds like you have a situation in which each file contains a matrix variable A and you want to load into memory the concatenation of all these matrices along some dimension. I had a similar need, and wrote the following function to handle it.

function var = loadCat( dim, files, varname )
%LOADCAT Concatenate variables of same name appearing in multiple MAT files
%  
%   where dim is dimension to concatenate along,
%         files is a cell array of file names, and
%         varname is a string containing the name of the desired variable

    if( isempty( files ) )
        var = [];
        return;
    end
    var = load( files{1}, varname );
    var = var.(varname);

    for f = 2:numel(files),

        newvar = load( files{f}, varname );
            if( isfield( newvar, varname ) )
                var = cat( dim, var, newvar.(varname) );
            else
                warning( 'loadCat:missingvar', [ 'File ' files{f} ' does not contain variable ' varname ] );
            end
        end 

    end

score 0 · Answer 3 · edited May 23 '17 at 10:28

Clark's answer and function actually solved my situation perfectly... I just added the following bit of code to make it a little less tedious. Just add this to the beginning and get rid of the "files" argument:

[files,pathname] = uigetfile('*.mat', 'Select MAT files (use CTRL/COMM or SHIFT)', ...
   'MultiSelect', 'on');

Alternatively, it could be even more efficient to just start with this bit:

[pathname] = uigetdir('C:\');
files = dir( fullfile(pathname,'*.mat') );   %# list all *.mat files
files = {files.name}';                       %# file names

data = cell(numel(files),1);                 %# store file contents
for i=1:numel(files)
    fname = fullfile(pathname,files{i});     %# full path to file
    data{i} = load(fname);                   %# load file
end

(modified from process a list of files with a specific extension name in matlab).

Thanks, Jason

Load Multiple .mat Files to Matlab workspace

3 Answers3

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