Create new algorithm for subgroup list generation

[Fletchersan]

Tell us about the problem you're trying to solve

Current subgroup generation algorithm, generates all possible subgroup algorithms. This is often time consuming and scales poorly.

Describe the solution you'd like

An alternate algorithm simply looks at all the unique subgroup combinations in the existing data. This is efficient especially when the number of subgroups are less wrt to all the possible subgroups.