CODEWITHSUNDEEP
python
fattmagan
fattmagan

Reputation: 51

How to return sum of matching elements in two separate sets

I have two sets with strings, and I want to be able to compare set1 elements with set2 elements, and output a sum of the matching elements. If I can avoid a loop with this, that would be preferred as well. The idea is like this:

   set1 = ['some','words','are','here']
   set2 = ['some','words','are','over','here','too']

The function I'm looking for would output a 4 here - returning True for all elements in set1 contained in set2. A likewise function in R would be

   sum(set1 %in% set2)

But I can't find an equivalent in Python. Let me know if any of you guys can help. Cheers

Upvotes: 1

Views: 348

Answers (1)

juanpa.arrivillaga
juanpa.arrivillaga

Reputation: 95948

First, you do not have a set objects, you have list objects:

>>> set1 = ['some','words','are','here']
>>> set2 = ['some','words','are','over','here','too']
>>> type(set1), type(set2)
(<class 'list'>, <class 'list'>)
>>>

Python supports set-literals which look like with curly braces:

>>> set1 = {'some','words','are','here'}
>>> set2 = {'some','words','are','over','here','too'}
>>> type(set1), type(set2)
(<class 'set'>, <class 'set'>)

Python set objects overload the bitwise operators to perform set-operations. You want the number of elements in the set intersection, so use the bit-wise and operator:

>>> set1 & set2
{'are', 'here', 'words', 'some'}
>>> len(set1 & set2)
4

Alternatively, you can use a more object-oriented style:

>>> set1.intersection(set2)
{'are', 'here', 'words', 'some'}
>>> len(set1.intersection(set2))
4

I prefer the operators, personally:

>>> set1 & set2 # intersection
{'are', 'here', 'words', 'some'}
>>> set1 | set2 # union
{'some', 'here', 'words', 'too', 'over', 'are'}
>>> set1 - set2 # difference
set()
>>> set2 - set1 # difference
{'too', 'over'}
>>> set2 ^ set1 # symmetric difference
{'over', 'too'}

If you have list objects, just convert to a set:

>>> l1 = ['some','words','are','here']
>>> l2 = ['some','words','are','over','here','too']
>>> set(l1).intersection(l2)
{'some', 'are', 'words', 'here'}
>>> len(set(l1).intersection(l2))
4

Upvotes: 2

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