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I'm a beginner trying to create a small Python project to help me find out which ingredient I might be allergic to from a group of four products. Ideally, I would like to input the ingredients of each product into a list format, and then return identical ingredients which appear in two or more of the products.

I'd like to input something like:

product_1 = ["polybutene", "cranberry seed oil", "beeswax"]
product_2 = ["vegetable oil", "beeswax", "shea butter"]

and get a result like:

list1 = ["beeswax"]

I've tried to use compare_intersect but haven't made any progress. Thank you very much in advance!

green_thumb
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1 Answers1

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If you want a list out you can do

list(set(product_1).intersection(set(product_2)))

Factored out to make each operation clear this looks like

set_1 = set(product_1)
set_2 = set(product_2)

intersection = set_1.intersection(set_2)

result = list(intersection)

If you want to preserve duplicates you can implement this efficiently like so.

from collections import Counter
def list_intersection(l1, l2):
  c2 = Counter(l2)
  result = []
  for element in l1:
    if c2[element] > 0:  # There are still more of those elements in the other list
      # The element is shared between the lists
      result.append(element)
      c2[element] -= 1
  return result

This will preserve the order of the first list, while only keeping the number of elements of the same type shared between the lists. Here's an example

list_intersection(['beeswax', 'test', 'other', 'beeswax', 'beeswax'],
                  ['frank', 'green', 'test', 'beeswax', 'beeswax'])


prints: ['beeswax', 'test', 'beeswax']
Marcel
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