I want to generate all possible combinations of provided input data. Lets take an example data set of {a, b, c, d}. There are 15 combinations possible with this data set, with different lengths. 

• Length 1:
  (a), (b), (c), (d)

• Length 2:
  (a, b), (a, c), (a, d), (b, c), (b, d), (c, d)

• Length 3:
  (a, b, c), (a, b, d), (a, c, d), (b, c, d)

• Length 4:
  (a, b, c, d)

How can we generate these combination is smart and easiest way in Pega ?