How to delete or exclude an entire matrix if it contains all zeros

I'm reading a large data set where sometimes there is a matrix of all zeros in all rows and columns. How do I either delete the entire matrix of zeros after it has been read, or exclude MATLAB from saving it in the first place?

Answer 1

[William Rose]

@Caitlin, you'll have to be more specific about how you are reading in the data in order to get a useful answer.

X=zeros(10,10);
whos            % show variables in the workspace

  Name         Size            Bytes  Class     Attributes

  X           10x10              800  double              
  cmdout       1x33               66  char                

You can delete variable X with

clear X
whos

  Name        Size            Bytes  Class    Attributes

  cmdout      1x33               66  char               

The output from whos shows that X is gone now.

[William Rose]

@Caitlin, if you're not sure if a matrix is all zeros, you can check quickly with

any(X,'all')

Example:

X=zeros(10,10);
Y=X; Y(4,6)=1e-6;
any(X,'all')   % returns 0 iff all elements of X=0

ans = logical
   0

any(Y,'all')

ans = logical
   1

You asked "How do I either delete the entire matrix of zeros after it has been read, or exclude MATLAB from saving it in the first place?" If, by "saving", you mean "having the variable in the workspace", then you can't exclude that, if you don't know ahead of time, because you must read it in to find out whether it is all zeros. Then you can check it and clear it, if desired.

[Caitlin]

@William Rose Thank you so much! Very helpful.

[William Rose]

@Caitlin, you're welcome.

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