How to split a matrix in different sections in a loop?

Hi all, I have to pick a particular section of a matrix A in each iteration of a loop and use that section for getting some results, i.e.

clear all
A=[ 1 2 3 1; 4 5 6 1; 2 3 4 2; 5 6 7 2; 8 9 3 2; 5 1 2 4; 7 8 1 4];
a=unique(A(:,4));
for j=1:size(a)
rho=a(j);
% B=...               for j=1, a(1)=1, then I should select B=[1 2 3 1; 4 5 6 1];
                      %for j=2, a(2)=2, then I should select B=[2 3 4 2; 5 6 7 2; 8 9 3 2];
                      %for j=3, a(3)=4, then I should select B=[5 1 2 4; 7 8 1 4];

%use B to compute some quantities...

end

The last column of B has values in ascending order, not necessarily equidistant among each other and not necessarily repeated the same number of times. I would like to avoid loops. Could you help me? Thanks!

Answer 1

[Jos (10584)]

    A=[ 1 2 3 1 ; 
        4 5 6 1 ; 
        2 3 4 2 ; 
        5 6 7 2 ; 
        8 9 3 2 ; 
        5 1 2 4 ; 
        7 8 1 4  ];
    UniqueA=unique(A(:,4)) 
    for j=1:numel(UniqueA)
       tf = A(:,4) == UniqueA(j)
       tmpB = A(tf,:) % select from A
       % .. some calculations on tmpB here ..
    end