Compare two lists of floats where order and duplicates matter in Python

Question

I want to compare the position and the differences in value between the two lists. I need to know how similar listB is to listA , not just does it contain the same values, but are those values in the same positions.

from collections import Counter

listA = [0.01, 0.02, 0.04, 0.03]
listB = [0.01, 0.02, 0.03, 0.04]

def compareListMethod1(a, b):
    return set(a).intersection(b)

def compareListMethod2(a, b):
    c1 = Counter(a)
    c2 = Counter(b)
    diff = c1-c2
    return list(diff.elements())

def compareListMethod3(a, b):
    count = Counter(a) # count items in a
    count.subtract(b)  # subtract items that are in b
    diff = []
    for x in a:
        if count[x] > 0:
           count[x] -= 1
           diff.append(x)
    return diff

print(compareListMethod1(listA, listB)) # returns {0.02, 0.01, 0.04, 0.03}
print(compareListMethod2(listA, listB)) # returns []
print(compareListMethod3(listA, listB)) # returns []

The desired output would reveal how many times the two lists were different from one another. In this case, the first two entries are exact, but the entries at index 2 and 3 are different - so there exist 2 differences between the two lists.

Thank you for any and all guidance!

Answer 1

If I understand correctly, this should work:

sum(a != b for a, b in zip(listA, listB))

Gives expected output of 2 .

Note that because your problem description states that order is important, sets will be no use here as they are not ordered.