I think I’m along the right lines but probably missing a function or two. To explain what I want I have my initial watch node which is producing a list of elements in my Revit window grouped together by their Z axis. As a result each sublist could range from how many elements are within it. In the watch node there is a total of 27 groups. Within each of these is a collection of Revit Elements with the parameter Number already embedded within. I have created a sequence of 1-28 which I then want to apply to each element within the corresponding group. So the first three elements in group 0 are assigned the value 1. The next four elements in the next group (1) are assigned the value 2 and so on. With the method pictured it seems to apply the values 1, 2, 3 to the first three elements and then for the next four elements starts again at 1, 2 , 3, 4.