amingilani amingilani - 1 year ago 106
Ruby Question

Intersections and Unions in Ruby for sets with repeated elements

How do we get intersections and unions in Ruby for sets that repeat elements.

# given the sets
a = ["A", "B", "B", "C", "D", "D"]
b = ["B", "C", "D", "D", "D", "E"]

# A union function that adds repetitions
union(a, b)
=> ["A", "B", "B", "C", "D", "D", "D", "E"]

# An intersection function that adds repetitions
intersection(a, b)
=> ["B", "C", "D", "D"]

, and
operators seem to ignore repetitions and duplicates, as written in the documentation.

# union without duplicates
a | b
=> ["A", "B", "C", "D", "E"]

# intersections without duplicates
a & b
=> ["B", "C", "D"]

Answer Source
def union(a,b)
  (a|b).flat_map { |s| [s]*[a.count(s), b.count(s)].max }

  # => ["A", "B", "B", "C", "D", "D", "D", "E"] 

def intersection(a,b)
  (a|b).flat_map { |s| [s]*[a.count(s), b.count(s)].min }

  #=> ["B", "C", "D", "D"]
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