Unable to load multiple mat files

Hello, I have a bunch of mat files as shown below. I feel I've done something similar before but now this is driving me slightly crazy...

I'm trying to load the data from the multiple mat files into a structure or any other easily indexable/accessible format.

This is my code

myFolder = 'C:\Users\dbhadra\Desktop\MSD\M150_Actuation_Accuracy\HittechProto3_RawData\output';
theFiles = dir(fullfile(myFolder, '/*M150*.mat'));
S = struct([]);
for i=1:numel(theFiles)
    S{i} = load(theFiles(i).name);
end

I keep getting errors, most common being below

Error using load
Unable to read MAT-file
C:\Users\dbhadra\Desktop\MSD\M150_Actuation_Accuracy\HittechProto3_RawData\output\2018-10-25_10-56-15_TEST_20_M150RawData_part1.mat.
Not a binary MAT-file. Try load -ASCII to read as text.

The funny is this seems to work standalone, except not in a loop. Where am I going wrong? Thanks.

Answer 1

[Jan]

This does not match:

S = struct([]);
for i=1:numel(theFiles)
    S{i} = ...    

You define S as a struct, but then you create cell elements. Either use S(i) or initialize S by:

S = cell(1, numel(theFiles));

The path is missing in the load command:

S{i} = load(fullfile(myFolder, theFiles(i).name));

But then the current folder must contain a file with the given name in a not matching format. This is at least strange.

Please openthe file manually and check the format. Are they ASCII-files?

[Deepayan Bhadra]

Hey @Jan: thanks for your reply. Even with

S(i) = load(fullfile(myFolder,theFiles(i).name));

I still get an error. Note that I was already in the folder where the .mat files are located. The above is overkill.

Subscripted assignment between dissimilar structures.

How do I tell if they are ASCII files? It just looks like an usual .mat file to me. When I load a single one in workspace. All the other .mat files are similar with varying no. of columns.

I even tried the alternate

S = cell(1, numel(theFiles));

but I still get the same error as in my original post.

[Jan]

"Note that I was already in the folder where the .mat files are located. The above is overkill." - no, it is not. Remember that a callback of a timer or GUI object can call cd() to change the current folder. This is a frequent source of run time errors, which are extemelly hard to debug. Therefore it is a good programming practice to use the absolute path in every case and not to use cd or relying on the current folder at all.

"How do I tell if they are ASCII files?" - Open the MAT file in an editor. You see directly, if this is ASCII (you can read everything) or binary (looking weird).

Of course storing the results in a cell does not solve the problem, that the MATfiles do not have the correct format to be imported.

[Deepayan Bhadra]

@Jan: "You see directly, if this is ASCII (you can read everything) or binary (looking weird)" -> seems to be binary but this contradicts the initial error that we see.

[Stephen23]

"but this contradicts the initial error that we see. "

No, it does not.

The error message states "Not a binary MAT-file."

Your file is a binary file, but that does not mean that it is a MATLAB MAT-file.

[Jan]

@Deepayan Bhadra: As Stephen said: This is not a binary MAT file. Binary MAT files starts with some readable text like "MATLAB 5.0 MAT-file, Platform: PCWIN64, Created on: Mon Feb 28 12:42:18 2022" before the binary stuff starts. Your file does not. So the error message is correct.

Which software has created the files?

Answer 2

[Stephen23]

theFiles is already a structure, there is no point in creating another one when you can use theFiles already:

myFolder = 'C:\Users\dbhadra\Desktop\MSD\M150_Actuation_Accuracy\HittechProto3_RawData\output';
theFiles = dir(fullfile(myFolder, '*M150*.mat'));
for k = 1:numel(theFiles)
    theFiles(k).data = load(theFiles(i).name);
end
data = [theFiles.data] % optional, assumes all file contain the same variables.

[Deepayan Bhadra]

Hi Stephen, I tried this, even removing the / from the .mat filename. Still the same error

Not a binary MAT-file. Try load -ASCII to read as text.

[Stephen23]

"Still the same error"

Still the same files: not binary MAT files.