How can i loop a matrix without knowing is size?

Hello!

So, i'm trying to make a loop where i have a matrix to go through and save their elements in a vector. Just note that i don't know the size of the matrix. So how can i do it?

Thanks!

[Star Strider]

Are you somehow prevented from using the size function?

[Joana Santos]

No, i just didn't know how to use :D

Answer 1

[Bob Thompson]

So, you have two matrices, one outside the loop, and one inside? Which one are you not sure about the size of?

If it is the outside loop you can set the loop bounds to be dependent on the size of the matrix.

for i = 1:size(mat,1) % (mat,1) for rows, (mat,2) for columns and so on

[Joana Santos]

Yes, that's it!

So it will be something like this... ?

mat = [ 1 2 3 ; 4 5 6]

v = zeros(1,6)

for i = 1: size(mat,1)

v(i) = mat(i)

end

P.S: i want this: v = [1 2 3 4 5 6]

[Joana Santos]

(In this case i know the size of the matrix but it's just an example)

[Bob Thompson]

Not quite. Using size in this manner will only loop through one dimension. Because you have two dimensions in 'mat' then you would actually need to do two loops, one for each direction.

However, because you are just trying to reorganize your data into a single dimension you can actually just use the reshape function.

v = reshape(mat,[n,1]);

[Joana Santos]

This is just an example. I pretend to use this code in a more complex function, but i need some bases...

I made this, but i still don't get the result. Where am i wrong?

mat = [ 1 2 3 ; 4 5 6]

v = zeros(1,6)

for i = 1: size(mat,1)

for j = 1:size(mat,1)

v(i) = mat(i,j)

end

end

[Bob Thompson]

It's your indexing for v. Your i loop only goes from 1:2, so indexing v with (i) will just give you v(1) or v(2). You need to change this to be a combination of i and j.

v((i-1)*size(mat,2)+j) = mat(i,j);

Also, you need to change your dimension your specifying for the innner loop. When you call size() the first input is the matrix, and the second input is the dimension. 1 is rows, 2 is columns, 3 is sheets, etc.

[Joana Santos]

Thank you so much! You helped me a lot :)

Have a nice day xx