cut of zeros from a matrix based on the longest non-zero row

Hi all,

I want to cut all zeros from the right, based on "the longest non zero row". an example:

A=[ 1 2 0 0 0 0;3 4 5 0 0 0;5 6 0 0 0 0];

output: A=[ 1 2 0 ;3 4 5 ;5 6 0 ];

thanks in advance!

[Yongjian Feng]

Try it yourself first please. We can then look at the code together.

Answer 1

[Dave B]

Another way to phrase this question is to say you want to remove columns from the right side of the matrix if the whole column is zeros:

A=[ 1 2 0 0 0 0;3 4 5 0 0 0;5 6 0 0 0 0];
lastnonzero=find(any(A~=0,1),1,'last') % the last column with a non-zero row

lastnonzero = 3

A(:,lastnonzero+1:end)=[]

A = 3×3

1 2 0 3 4 5 5 6 0

[Nikolas Spiliopoulos]

thanks a lot!!

[Net Fre]

OK, much better than mine :)

Didn't know about any. Notice that your code will ingore non-zero negatives.

[Dave B]

oops, I updated to be ~=0, thanks for catching that! (technically it can just be any(A), but I find that specifying the condition explicitly is more readable)

any and all are very useful! they also take a dimension arg, or the keyword 'all' which I use often.

Answer 2

[Net Fre]

Hi

You can use the cumprod function.

your code line can look like this:

% a = some matrix
idx = max(sum(cumprod(a~=0,2)),2)
output = a(:,1:idx)

I suggest you break the one line into several ones just to see what each function does.

hope this helps.