Python – Sum of each List element occurrence in another

Sometimes, while working with Python, we can have a problem in which we need to get occurrence of 1 element in another. But as a modification of this, we can have a problem in which we need to count the occurrence of all elements of 1 list in another. Lets discuss certain ways in which this task can be performed.

Method #1 : Using nested loops
This is one of the way in which this task can be performed. This is brute force way in which this task can be performed. In this, we iterate one list and then target list, if element match, we increase the counter.

# Python3 code to demonstrate
# Sum of each List element occurrence in another
# using nested loops

# Initializing lists
test_list1 = [1, 3, 4, 5, 1, 4, 4, 6, 7]
test_list2 = [4, 6, 1]

# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))

# Sum of each List element occurrence in another
# using nested loops
res = 0
for ele in test_list2:
    for ele1 in test_list1:
        if ele1 == ele:
            res = res + 1

# printing result
print ("The occurrence count : " + str(res))

Output :

The original list 1 is : [1, 3, 4, 5, 1, 4, 4, 6, 7]
The original list 2 is : [4, 6, 1]
The occurrence count : 6

Method #2 : Using sum() + count()
The combination of above methods can be used to perform this particular task. This is one liner alternative to the above method. In this counting is done using count() and accumulation using sum().

# Python3 code to demonstrate
# Sum of each List element occurrence in another
# using sum() + count()

# Initializing lists
test_list1 = [1, 3, 4, 5, 1, 4, 4, 6, 7]
test_list2 = [4, 6, 1]

# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))

# Sum of each List element occurrence in another
# using sum() + count()
res = sum(test_list1.count(idx) for idx in test_list2)

# printing result
print ("The occurrence count : " + str(res))

Output :

The original list 1 is : [1, 3, 4, 5, 1, 4, 4, 6, 7]
The original list 2 is : [4, 6, 1]
The occurrence count : 6