Clearing workspace variables while in a loop.

I have a while loop that contains a menu and some options for the user to input. One of them is to delete the workspace variables. However, whenever I clear the workspace it doesn't actually clear until the while loop stops (this occurs when they exit the program).

% case 3 
    % Clear data from memory
    clearvars -except continueprogram % 
    % This clears the entire workspace, while allowing the 
    % program to continue running.
    %             
    clc;
    fprintf('The memory is cleared. Press a key to continue. \n')
    pause;

[Image Analyst]

Why would you want to clear variables while a loop is running? This does not seem like a wise thing to do. Please provide justification for doing this.

[Kyle Reagan]

The loop is a data analysis tool for an uploaded file. It does things like plot histograms, linear regression, etc. One of the options on my menu is "Clear All" so that the user can clear all the file data, and then upload a new file without ever having to exit from the program.

[Stephen23]

Clearing variables in a loop seems like an inefficient way to write code. Either the variables are re-allocated in each iteration (in which case clearing them serves no purpose) or new variables are created on each iteration (in which case the code is going to be buggy and slow no matter what).

Clearing variables is slow. Code of this complexity should be written as a function (and not a script), in which case it is totally irrelevant to the end user what variables exist in the function workspace.

Answer 1

[Walter Roberson]

How can you tell that the workspace is not actually cleared?

If you are using the Workspace Browser then you need to know that (at least in recent versions) the Workspace Browser is not updated until you stop in the debugger or use keyboard() or control returns to the command line.

[Kyle Reagan]

I created a variable "a = 5" in the command window. Then I ran my loop which functions through a menu with various options. It has a pause feature after each action. So after I pressed "Clear All" on the menu ("clearvars -except continueprogram" is how it works), I did "5*a" in the command window and got 25.

[Walter Roberson]

https://www.mathworks.com/help/matlab/ref/clearvars.html

"clearvars removes all variables from the currently active workspace."

You are clearing the variables from the workspace of the callback function, which is not touching the variables of the base workspace.

[Kyle Reagan]

Whenever I use any type of clear the same thing happens. Do you know of a way to clear the base workspace while the loop continues?

[Walter Roberson]

evalin('base', 'clear')

[Kyle Reagan]

This clears the "continueprogram = true" variable and causes the loop to stop running.

[Walter Roberson]

evalin('base', 'clearvars -except continueprogram')