Algorithm 1 A recursive algorithm for DAG clustering

Input   :iter—map that stores the iteration count of the corresponding dataset or cluster

root—top node in DAG

Output: clusters—a set of clustered nodes

1: function clustering

2:     ▹ Recursively traverse all nodes in DAG

3:     cluster $\leftarrow \left\{\mathit{root}\right\}$

4:     descs $\leftarrow \left\{\mathit{root}\right\}$

5:     while descs $\ne ⌀$ do

6:         desc = descs.pop

7:         if iter[desc] == iter[cluster] then

8:               descs $\leftarrow \mathit{descs}\cup \mathit{desc}.children$

9:               cluster $\leftarrow \mathit{cluster}\cup \left\{\mathit{desc}\right\}$

10:         else

11:               clusters $\leftarrow \mathit{clusters}\cup \left\{\mathit{cluster}\right\}$

12:               clusters $\leftarrow \mathit{clusters}\cup clustering\left(\mathit{desc}\right)$

13:               cluster $\leftarrow ⌀$

14:         end if

15:     end while

16:     return clusters

17: end function