How to reset a MultiDimensional Array to allow a fresh building of the MDA

Hello.

I am trying to find statistical variations between upto 10 matrices. the idea is everytime I run my code via a pushbutton, a file containing a matix is loaded and then added to a multi-dimensional array via the 3rd argument that I call "page". At the end I perform elementwise statistics, but need the option to start again. Hence i have another button to "reset" the MDA. Im therefore declaring my multidimensional array MDA as global.

At the start iof my pushbutton function I have

global MDA                   % Needs to be global as I have another pushbutton that resets the MDA
[x,y,page]=size(MDA)         % I then determine the current size (in the 3rd dimension)
MDA(:,:,page+1)=data         % Add the latest data (just read from file)
max1=max(MDA,[],3)           % Get elementwise max of the data
min1=min(MDA,[],3)           % Get elementwise min of the data

Then in a reset pushbutton callback I have

global MDA;
MDA=[];

But when I do a size on this,

 [x,y,page]=size(MDA)

page is 1.

I really need the reset to put page=0 as my MDA would otherwise contains zeros in the first page, unless there is a better way to do this

Thanks

Jason

Answer 1

[Jon]

There may be some cleaner way to do this, but I would suggest that one approach would be to use an if statement to test if MDA is empty and if it is start a new one. So somthing like

if ~isempty(MDA)
    % normal case, append to existing MDA

    [x,y,page]=size(MDA)         % I then determine the current size (in the 3rd dimension)
    MDA(:,:,page+1)=data         % Add the latest data (just read from file)
else
    % new multidimensional array
    MDA(:,:,1)=data         % Add the latest data (just read from file)
end
max1=max(MDA,[],3)           % Get elementwise max of the data
min1=min(MDA,[],3) 
    
end

You could also put the call to size before the if-else and then branch based on whether page == 1

This would save a call to isempty, but would reduce the readability of the code as the intent might be a little less obvious. Actually I was surprised that the size of the third dimension of an empty array is 1 and not zero, but apparently that is how they implemented the size function. I think it would be better practice to just check if MDA is empty using isempty

[Jason]

Yes thats what messed me up, when you reset, the "page" still remained 1.

Thnaks for your help