removing zero element rows in a m×n matrix?

i want to remove the rows which contain all zeros. so finally i expect a matrix containing with the remaining rows. I use a 'for loop' to represent each row, but then i get a error "Index of element to remove exceeds matrix dimensions". help me to get rid of these zero elemental rows. thank you. example: a =[0 0 0 0

    1 2 3 4
    2 0 1 1
    0 0 0 0]

new_a =a;

for i=1:4

 if a(i,:)==0 

   new_a(i,:)=[];

 end 
end 
new_a

Answer 1

[Walter Roberson]

That is a common error. After you assign [] to remove a row, the matrix now has fewer rows, but you proceed as if it still has as many rows as it used to have. Eventually you will index a row that no longer exists.

Easiest fix: loop backwards, so that the rows you have not examined yet will not have been moved.

Better fix: use logical indexing and do everything at the same time:

new_a = a(any(a,2),:);

or

new_a = a;
new_a(~any(a,2),:) = [];

[Rakesh Praveen]

Thanks now its working. when u say any(a,2) what does the 2 mean ?

[Walter Roberson]

The 2 means to work across the second dimension, which is across rows in MATLAB. The first dimension is columns and is the default direction for the majority of MATLAB operations.