How to select a column on basis of some conditions on the rows?

I have a situation where I have a 6x100 matrix like the one below:

x = randn(6,100)

What I would like to do is to write a code that says: for every column in x keep only those columns whose first and second rows have positive entries, while the fourth one has a negative entry. So let's take two representative columns like the ones below:

0.5     0.3
3.1     0.2
0.6     0.6
0.8     -0.9
0.1     -1
0.3      1

The code should exclude the first column and keep the second; this for every column in x.

Can anyone help me with that?

Thanks!

Answer 1

[Timo Dietz]

Does this solve your problem?

x = x(:, x(1, :) > 0 & x(2, :) > 0 & x(4, :) < 0)

[Armando MAROZZI]

thanks a lot! Easier than thought once I see it ! thanks again