Using Indexing from values in another vector

Hello all,

I have a vector called i, where for example

 i = [1 1 2 3 3]';

and I have a vector n, where

 n = [2 1 2]'

corresponds to the number of values in i. So n(1) corresponds to the number of 1's in i, n(2) corresponds to the number of 2's in i, etc. I also have another vector j, where j also has values like

 j = [1 3 2 2 3].

My question is how could I use the vector n to access the elements in j? Basically I want to use the first two elements of j since n(1) = 2, then I want to access the second element since n(2) = 1 and finally the last two elements of j since n(3) = 2.

Answer 1

[Azzi Abdelmalek]

i = [1 1 2 3 3]';
n = [2 1 2]';
j = [1 3 2 2 3];
idx2= cumsum(n);
idx1=[1; idx2(1:end-1)+1];
for k=1:numel(idx1)
  s{k}=j(idx1(k):idx2(k))
end