How to get the duplicates between two lists that and make a list with only the duplicates? (Assuming-CodePudding

EX:

list1 = [1,2,3,4,5]
list2 = [1,2,8,4,6]

# Now we want to get the duplicates
# ...
# Add them to a list:

duplicates = [1,2,4]

I tried to search but I only found how to remove the duplicates.

CodePudding user response：

By converting one of the lists to a set prior to picking members, this operation will run in linear time - rather than in quadratic time.

That can make a huge difference if both lists starts to get to the hundreds of thousands of items:

set1 = set(list1)
duplicates = [item for item in list2 if item in set1]

otherwise, for just a handful of items, a simple filter is enough: duplicates = [item for item in list2 if item in list1].

CodePudding user response：

You can use a set and the .intersection method. Like this:

list1 = [1,2,3,4,5]
list2 = [1,2,8,4,6]

duplicates = list(set(list1).intersection(list2))
print(duplicates)  # => [1, 2, 4]