How to solve this simple index problem

Hi, I have

a=[1;2;3]and b=[23;nan;4]

how I can get these

c=[2] and also D=[1,23;3,4]

Thanks a lot

Answer 1

[Walter Roberson]

idx = isnan(b);
c = a(idx);
D = [a(~idx), b(~idx)];

[Rita]

Thanks a lot Walter