Python：如果有重复项，如何查找两个列表的交集（实际上，我需要一个交集的长度）？

Question

Let me have thse two lists:

a = ['a','b','c','a','a']
b = ['a','b','d']

I need to calculate Jaccard distance = (union-intersect)/union, but I know there gonna be duplicates in each list, and I want to count them, so intersect lenght for the example would be 2 and Jaccard distance = (8-2)/8

How can I do that? first thought is to joint lists and then remove elements one by one...

UPDATE: probably I had to stress more that I need to count dublicates;

here is my working solution, but it is quite ugly:

a = [1,2,3,1,1]
b = [2,1,1, 6,5]

import collections
aX = collections.Counter(a)
bX = collections.Counter(b)

r1 = [x for x in aX if x in bX]
print r1

print sum((min(aX[x], bX[x]) for x in r1))

>>> 3

Answer 1

a = ['a','b','c','a','a']
b = ['a','b','d']
c = list(set(b).intersection(a))
['a','b']

Note sets will discard duplicates!

Answer 2

To the get the jaccard index between two lists a and b:

def jaccard_distance(a,b):
    a = set(a)
    b = set(b)
    c = a.intersection(b)
    return float(len(a) + len(b) - len(c)) /(len(a) + len(b))

Answer 3

here is my working solution, but it is quite ugly:

a = [1,2,3,1,1]
b = [2,1,1, 6,5]

import collections
aX = collections.Counter(a)
bX = collections.Counter(b)

r1 = [x for x in aX if x in bX]
print r1

print sum((min(aX[x], bX[x]) for x in r1))

>>> 3