Load, Process, Rename and Save Multiple Files

Dear Matlabers,

I know in the Matlab FAQ there's a very popular solution to how to load multiple files, but it doesn't help me, as I can't convert it into my specific problem.

I have files named file1.mat, file2.mat and file3.mat. I want to load the files into matlab, then multiple each file by a number and save them with as filenames fileprocessed1.mat, fileprocessed2.mat and fileprocessed3.mat respectively.

Thanks so much for your help and have a nice day.

[Guillaume]

a .mat file is a file that can contain any kind and number of variables, including strings, objects, function handles, structures, cell arrays, etc.

What does "multiplying a file by a number" mean in that contest?

Is it all the variables in each .mat file that you want to multiply? Do the variables have the same names in the each file?

[AT]

Dear Guillaume,

Indeed, there's information missing. My mat files are 70x1 doubles, or single column matrices. I want to multiply each value of that matrix by 5, and this for every single matrices I have.

Thank you.

Answer 1

[Guillaume]

folder = 'c:\somewhere\somefolder';
numfiles = 100;
multiplier = 5;
for fileidx = 1:numfiles
   oldcontent = load(fullfile(folder, sprintf('file%d.mat', fileidx));
   newcontent = structfun(@(m) m * multiplier, oldcontent);
   save(fullfile(folder, sprintf('fileprocessed%d.mat', fileidx)), '-struct', 'newcontent');
end

is one way to do it. Instead of generating the names of the file to read you can also obtain them with dir if you prefer.

Because load is assigned to a variable, the original variables of the .mat file are transformed into fields of the oldcontent structure. I use structfun to multiply each field of the structure by your constant and create a new structure with the same field names. save with the '-struct' option then save the fields of the structure back as variables.

[AT]

Thanks Guillaume, very kind. What is the fullfile in the load() function?

[Guillaume]

If you type

doc fullfile

or Press F1 with your cursor on the word, you get its documentation which explains what it does: "Build full file name from parts". Basically, it builds the path of the file, without you having to worry about the directory separator (/ on linux, \ windows).

[AT]

Dear Guillaume, Thanks again. Unfortunately, I can't get this to work.

My exact description of the problem is as follows:

I have the files: file26.mat file27.mat file29.mat file30.mat

Each file is a single column matrix of 70 values.

At the end I need all those matrixes multiplied by 5 and saved as

file26processed.mat file27processed.mat file29processed.mat file30processed.mat

Using your code, I get troubles with missing numbers and with reading the files in.

Again, I would really appreciate your help. I am still studying matlab.

Thanks!

[Guillaume]

Spend some time understand the code I've written. You're free to change the values that are passed to the loop (or as I've said you could obtain the list of files with dir as per the examples you said you've read).

In your case, this simple change should solve the problem:

for fileidx = [26 27 29 30]