Deleting within .mat file

Hello,

This is a screenshot of my MAT-file. How do you permantly delete certain structures? For example, if I want 'B' deleted.

I used to be able to right click on the one I wanted to delete, and it gave me options to delete, duplicate, move, etc, but one day it stopped letting me do that. Does anyone know why it no longer lets me delete right in that window? Is there something I need to enable?

Thanks!

Answer 1

[Matt J]

I don't remember that ever being possible through the Matlab GUI, but attached is a MEX file that can do it.

rmvarMatfileMEX('allData.mat','B')

[Walter Roberson]

If I recall properly, in v5 .mat to v7 .mat files, it is possible to mark a space as unused, effectively deleting it, but that the mechanism does not reclaim space.

[Sclay748]

I tried this one. Thought it was working because it was deleting the variables in the window, but when I went to save the .mat file, they all came back.

[Matt J]

If you saved the variables to the .mat file again, of course they came back... The idea is to not put the variables back in the .mat file once you've removed them.

[Sclay748]

But they are not being called/used in the script anywhere. Usually they only come back if they are in use, but the script changed and they are no longer used anywhere. Am I incorrectly assuming that?

[Matt J]

Do the following test and tell us the result,

clear all
rmvarMatfileMEX('allData.mat','B')
load allData

whos B

[Sclay748]

That still didnt work for me, but I did get it to work. I did a combination of:

rmvarMatfileMEX('allData.mat','B')

then at the bottom of the script:

clearvars B

Then it deleted B and I was able to save.

[Matt J]

What was the result of running the 4 lines of code that I posted in my last comment?

Your use of clearvars has nothing to do with the issue in your posted question. Your question is about removing B from a .mat file, not removing it from the Matlab wokspace. It is obvious and trivial that the .mat file will never contain B if you clear B before the .mat file is created. Your question is about removing B from the .mat file when it has already been put there by mistake.

[Sclay748]

It cleared B, but then the script said did not recognize a variable that was actually used and still included in the .mat file.

[Matt J]

Well, you need to show the full script in order for us say what's really going on. It sounds unrelated, though, to the issue in your post.

[Sclay748]

Unfortunatly I cant show it due to it being for work, but atleast the problem has fixed itself and the variables are deleting as expected. I'll figure things out and get better at Matlab slowly. Thank you for the help!

Answer 2

[VBBV]

Use clear command as e.g

clear B W X Y Z

or

clearvars B W X Y Z in your script file or the function file in the end line

So, when you save the workspace variables as *.mat they will not appear in the *.mat file when you load it back into workspace

[Walter Roberson]

is there documentation for that? I do not find it. https://www.mathworks.com/help/matlab/ref/clear.html

[VBBV]

Agree with you Walter, there is no documentation for it

[Sclay748]

I tried this one, but it did not work for me. I am just trying to clean the variables so it wouldnt be confusing when someone loads it later.

[VBBV]

Try

delete B W X Y Z

At the end of file

Answer 3

[Walter Roberson]

A work-around that is sometimes good enough is to create the variable locally with empty contents, and save with the -append flag. The old variable in the file will be marked as unused and the new empty variable will be saved in the file.

This does not completely remove the variable from the file: the variable name would still be there, just associated with empty content. But the previous content would no longer be associated with the name.