Trim Binary Matrix in MatLab

Question

I have a binary matrix like this:

0 0 0 0 0 0
0 0 0 1 0 0
0 1 0 0 0 0
0 0 1 0 1 0
0 0 0 1 0 0
0 0 0 0 0 0

and I want to trim this matrix (in other words, remove zeroes at the boundaries) to be like:

0 0 1 0
1 0 0 0
0 1 0 1
0 0 1 0

How to do this the "Matlab" way? that's not to use conventional loops and conditions.

To be clearer, the matrix should be reduced to start from the first column which has at least one 1, and ends at the last column with the same condition, inclusive. Any column out of this range should be removed. Same rules apply for rows.

Thanks.

Answer 1

If you have the data in matrix M...

x = find(any(M,2),1,'first'):find(any(M,2),1,'last');
y = find(any(M),1,'first'):find(any(M),1,'last');
M(x, y)

Or, if you know that there will be a 1 in every row/col except the edges:

M(any(M,2), any(M))

Answer 2

Extension to higher dimensions:

Assuming a 3D matrix to be trimmed, this is more straightforward:

M=rand(3,3,3); % generating a random 3D matrix
M(2,:,:)=0; % just to make a check if it works in extreme case of having zeros in the         middle

padded = padarray(M,[2 2 2]); % making some zero boundaries

[r,c,v]=ind2sub(size(padded),find(padded));

recoveredM=padded(min(r):max(r),min(c):max(c),min(v):max(v));

check=M==recoveredM  % checking to see if M is successfully recovered