Combining two lists and removing duplicates, without removing duplicates in original list

user_80943 0
Viewed 261049

I have two lists that i need to combine where the second list has any duplicates of the first list ignored. .. A bit hard to explain, so let me show an example of what the code looks like, and what i want as a result.

first_list = [1, 2, 2, 5]

second_list = [2, 5, 7, 9]

# The result of combining the two lists should result in this list:
resulting_list = [1, 2, 2, 5, 7, 9]

You'll notice that the result has the first list, including its two "2" values, but the fact that second_list also has an additional 2 and 5 value is not added to the first list.

Normally for something like this i would use sets, but a set on first_list would purge the duplicate values it already has. So i'm simply wondering what the best/fastest way to achieve this desired combination.

Thanks.

list python
12 Answers

You can bring this down to one single line of code if you use numpy:

a = [1,2,3,4,5,6,7]
b = [2,4,7,8,9,10,11,12]

sorted(np.unique(a+b))

>>> [1,2,3,4,5,6,7,8,9,10,11,12]
user_42761120

Simplest to me is:

first_list = [1, 2, 2, 5]
second_list = [2, 5, 7, 9]

merged_list = list(set(first_list+second_list))
print(merged_list)

#prints [1, 2, 5, 7, 9]
user_36004870

Based on the recipe :

resulting_list = list(set().union(first_list, second_list))

user_35927510

you can use dict.fromkeys to return a list with no duplicates:

def mergeTwoListNoDuplicates(list1, list2):
    """
    Merges two lists together without duplicates
    :param list1:
    :param list2:
    :return:
    """
    merged_list = list1 + list2
    merged_list = list(dict.fromkeys(merged_list))
    return merged_list
user_90794110
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