How can I get the intersection union and subset of arrays in Ruby

Question

I want to develop many methods for the Multiset class.

I am unsure of how to write intersection, union, and subset methods, while I have all the necessary methods.

My code begins with: "My code starts with intersection and union."

def intersect(var)
  x = Multiset.new
end

Take this example

X = [1, 1, 2, 4]
Y = [1, 2, 2, 2]

Here, intersection would be [1,2]