selecting desired values

i gave some data

column1    column2    

1,1         3,4
1,2
1,3
;
;
;
1,100       3,100
2,1
;
;
;
2,100          4,100

I want to select 15 values from each 100 ,the values in column should not change,,

(i.e) 1,1..1,15...2,1...2,15...3,1...3,15...4,1..4,15

can u tell how to process

Answer 1

[Andrei Bobrov]

[j1,i1] = ndgrid(1:100,1:4);
ind = [i1(:) j1(:)];

somedata = ind(randperm(numel(i1)),:);
idx = bsxfun(@plus,(1:15)',0:100:numel(i1)-1);
out = somedata(idx,:);

Answer 2

[Lulu]

Do you want to select values based on indices? If so, then here is an example: ind = [1; 2; 5; 15]; col1 = array(ind,1); col2 = array(ind,2);

[FIR]

not on indices first 15 from 100 without changing value in columns