Given an array like
[0, 3, 7, 22, 6, 71, 1, 0, 9]
how do you sum up the first group of three elements (0+3+7), the second group of three elements (22+6+71), the third group (1+0+9), and so on and so on, without using a Repeat node?
Well, you could write your own custom ICE node. Or you could use Generate Sample Set like this:
eX-SI 
had to take route ‘a’ because I needed the node to work per point. Shared here for your convenience *:)
http://www.si-community.com/community/viewtopic.php?f=19&t=4936