Find indices in 2D Matrix

Hello everyone,

I'm trying to solve he problem with my indices. I have a 2D matrix A with ones and zeros. Now i want to define my other matrix B on those coordinates where A=1. But in the end i still want to have an 2D Matrix, not a vector with indeces.

Does anyone know how this could be solved.

Thank you!

A = rand(50,20)>.3;
B=rand(50,20);

newmatrix=B(A);

Answer 1

[the cyclist]

Is this what you mean? (I made the matrices smaller, just to show the result.)

A = rand(5,2)>.3;
B = rand(5,2);

newmatrix = zeros(size(A));
newmatrix(A) = B(A)

newmatrix = 5×2

0.5006 0 0.1912 0.2603 0.9736 0.3731 0 0.7064 0 0

[Bianka Markovic]

Thank you for the answer! Really appreciate it.

Yes, this helps a lot thank you!

[Bianka Markovic]

Oh, I have one more question. If I have now a second matrix, which is for example C=(5,2,6) how can I use the idices from before for the two dimensions and take all other values from the third dimension?

[the cyclist]

You can do

newC = C .* A;

which made me realize that the much easier way to do your original problem is

newmatrix = B .* A;

[Bianka Markovic]

Hm, it says that the matrix dimension must agree. But I made it with D = bsxfun(@times,C,B); :) Thanks again!

[the cyclist]

Ah, sorry. You must have an older version of MATLAB. Newer versions (since R2016b) have implicit expansion. Glad you found bsxfun.