[matlab] How to delete zero components in a vector in Matlab?

I have a vector for example

a = [0 1 0 3]

I want to turn a into b which equals b = [1 3].

How do I perform this in general? So I have a vector with some zero components and I want to remove the zeroes and leave just the non-zero numbers?

Data

a=[0  3   0   0   7   10   3   0   1   0   7   7   1   7   4]

Do

aa=nonzeros(a)'

Result

aa=[3   7   10   3   1   7   7   1   7   4]

I just came across this problem and wanted to find something about the performance, but I couldn't, so I wrote a benchmarking script on my own:

% Config:
rows = 1e6;
runs = 50;

% Start:
orig = round(rand(rows, 1));

t1 = 0;
for i = 1:runs
    A = orig;
    tic
    A(A == 0) = [];
    t1 = t1 + toc;
end
t1 = t1 / runs;

t2 = 0;
for i = 1:runs
    A = orig;
    tic
    A = A(A ~= 0);
    t2 = t2 + toc;
end
t2 = t2 / runs;

t1
t2
t1 / t2

So you see, the solution using A = A(A ~= 0) is the quicker of the two :)

b = a(find(a~=0))

Why not just, a=a(~~a) or a(~a)=[]. It's equivalent to the other approaches but certainly less key strokes.

You could use sparse(a), which would return

(1,2) 1

(1,4) 3

This allows you to keep the information about where your non-zero entries used to be.

I often ended up doing things like this. Therefore I tried to write a simple function that 'snips' out the unwanted elements in an easy way. This turns matlab logic a bit upside down, but looks good:

b = snip(a,'0')

you can find the function file at: http://www.mathworks.co.uk/matlabcentral/fileexchange/41941-snip-m-snip-elements-out-of-vectorsmatrices

It also works with all other 'x', nan or whatever elements.