MATLAB: How to select n rows every m rows

Question

It's a select several rows/extract rows in data question. My data looks like this:

a1 b1 c1
a2 b2 c2
a3 b3 c3
a10 b10 c10
a20 b20 c20
a30 b30 c30
a1 b1 c1
a2 b2 c2
a3 b3 c3
a10 b10 c10
a20 b20 c20
a30 b30 c30
a1 b1 c1
a2 b2 c2
a3 b3 c3
a10 b10 c10
a20 b20 c20
a30 b30 c30

I need to extract into a new data which only includes

a10 b10 c10
a20 b20 c20
a30 b30 c30
a10 b10 c10
a20 b20 c20
a30 b30 c30
a10 b10 c10
a20 b20 c20
a30 b30 c30

How can I do that? Thank you.

Answer 1

This will work for any m,n.

m=3;
n=3;
e=1:size(yourdata,1);
idx=e(  (m+n):(m+n):end  ) - (n-1:-1:0).'  ;
newdata = yourdata(idx,:);