I have four lists with their values:
A = [1,2,3,4,5,6,7,8,9,10]
B = [1,2,3]
C = [4,5,6]
D = [7,8,9,10]
Would you have some function to compare list A with the other three lists and say how many numbers from list A repeat with those from the next 3 lists? For example: List A contains 3 numbers from list B, list A contains 3 numbers from list C, list A contains 4 numbers from list D.
The set structure has the function intersection , which returns the intersection between set and another iterable element, such as a list. We can easily define a function that simply transforms one of the lists into a set and returns the size of the intersection (common elements) between one list and another:
A = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
B = [1, 2, 3, 5, 11]
def contagem_interseccao(a, b):
s = set(a)
return len(s.intersection(b))
print(contagem_interseccao(A, B)) # 4
You can convert both lists to set so you can use the intersection operator ( & ) to calculate the amount of elements in common between them:
A = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
B = [1, 2, 3, 5, 11]
n = len( set(A) & set(B) )
print( n )
Output:
4