MATLAB: If I have a matrix of data and I want to pull out certain data cells and arrange them in another matrix

data processing/filtering

More info:

I have a matrix of information and I want to pull certain data cells from all the rows beginning with a 20.

Of the rows starting with the number 20, I want the third cell over.

Ex. I want to grab the cells that are bolded.

10 40 50 80

20 40 20 34

30 50 32 50

20 38 40 36

I want to then take those data cells and put them into a 1 lined matrix

a=[10 40 50 80
20 40 20 34
30 50 32 50
20 38 40 36]
c=find(a(:,1)==20)
out= a(c,3)

[ii,ii] = sort(r(3:3:end));
out = reshape(r(bsxfun(@plus,ii*3,(-2:0)')),1,[]);

OR:

out = reshape(sortrows(reshape(r,3,[])',3)',1,[]);

One possible solution would be like this:

A = [50,20,30; 55,25,35; 60,30,40];
[p1,p2,p3] = ndgrid(1:3);
Result = [A(p3(:),1),A(p2(:),2),A(p1(:),3)];