A recursive approach to combine arbitrary number of vectors, real use case: compute the combination of SKU

vectors_combine_rec.py

# -*- coding: utf-8 -*-
"""
   The is a recusive approach solving the vectors combination problem
"""

# Y for yellow, G for green
# 1 2 3 4 for size
# H for heavy, L for light, O for overweight
vectors = [['Y', 'G'],
           [1, 2, 3, 4],
           ['H', 'L', 'O']]

level = 0


def combine(subvectors, level):
    if len(subvectors) > 0:
        holder = []
        for el in subvectors[0]:
            print(' ' * level, "{0} + comb({1})".format(el, subvectors[1:]))
            # el + following line
            comb = combine(subvectors[1:], level + 1)

            # Because we want a two dimensional result, 2d list + 2d list = 2d
            # list
            holder = holder + assemble(el, comb, level)
            print(' ' * level, "Level {0}: another elem".format(level))
        # Only print while all variable are included, no sub-set
        if level == 0:
            print(holder)
        return holder
    else:
        return []


def assemble(el, comb, level):
    """assemble elem and list together
        1 + [['H'], ['L'], ['O'] => [[1,'H'], [1, 'L'], [1, 'O']
        lift up, and keep it a two dimension list
    """
    if len(comb) == 0:
        # If no elem in comb, simply return the elem as list
        return [[el]]
    return [([el] + c) for c in comb]

if __name__ == "__main__":
    # Note that a combination does not necessarily to be a combination of
    # single elements.
    # If can also be a single element and other vectors
    # This the basis for recusion
    result = combine(vectors, level)