Python: How to generate list with items repeating in two lists

Question

I have two lists of items:

list_1 = ['A', 'B', 'C', 'C', 'D']
list_2 = ['C', 'C', 'F', 'A', 'G', 'D', 'C']

I want to create a new list with the elements that are in the two lists. Like this:

['A', 'C', 'C', 'D']

Notice that it should take in mind that any item can repeat in list several times and should be in the new list as many times as it is repeated in both lists. For instance, 'C' is repeated 2 times in list_1 and 3 times in list_2 so it appears 2 times in the result.

The classic method to do it will be:

import copy
result = []
list_2 = fruit_list_2.copy()
for fruit in fruit_list_1:
  if fruit in list_2:
    result.append(fruit)
    list_2.remove(fruit)

but I am interested to do it by generation lists: [number for number in numbers if number > 0]. Is it possible?

Why is `C` in the output then if it the counts are different? — yatu, Nov 08 '19 at 15:28
In new list need takes minimal times repeating = what exactly we have in two lists — Lzhelis, Nov 08 '19 at 15:44

score 3 · Answer 1 · answered Nov 08 '19 at 15:29

3

If you aren't terribly concerned about the ordering of the new list, you can use collections.Counter.

>>> list((Counter(list_1) & Counter(list_2)).elements())
['A', 'C', 'C', 'D']

& takes the intersection of the two as multi-sets, with the minimum count used for common elements. The elements method returns the items in the result as an iterator, hence the list wrapper`.

answered Nov 08 '19 at 15:29

chepner

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thanks! It is looks cool) and new for me. But i need do it by generating list.. ( – Lzhelis Nov 08 '19 at 21:57

score 2 · Answer 2 · answered Nov 08 '19 at 15:28

2

I think it's as simple as:

list_1 = ['A', 'B', 'C', 'C', 'D']
list_2 = ['C', 'C', 'F', 'A', 'G', 'D', 'C']

list_3 = [x for x in list_1 if x in list_2]

print(list_3)

# returns ['A', 'C', 'C', 'D']

answered Nov 08 '19 at 15:28

kjmerf

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This solution will not ensure the required number of times per input appearance. – Cristian Ramon-Cortes Nov 08 '19 at 15:36
Thank you! I tried, but it has error in case: fruit_list_1 = ['A', 'B', 'C', 'C', 'C', 'L', 'C'] fruit_list_2 = ['C', 'C', 'F', 'A', 'N', 'L', 'C'] new_list will be: ['A', 'C', 'C', 'C', 'L', 'C'] but need just 3C – Lzhelis Nov 08 '19 at 15:36
1

@kjmerf list_1 = ['A', 'A'], list_2 = ['A'] should have list_3 = ['A'] and your solution will provide list_3 = ['A', 'A'] – Cristian Ramon-Cortes Nov 08 '19 at 15:39
I guess I mis-understood the question. I thought we wanted duplicates. – kjmerf Nov 08 '19 at 15:40
1

I understand that entries must be duplicated as many times as they appear in both lists. So list_1 = ['A', 'A', 'A'], list_2 = ['A', 'A'] should have list_3=['A', 'A'] – Cristian Ramon-Cortes Nov 08 '19 at 15:42
I get it. Will leave the answer up but thanks for the explanation – kjmerf Nov 08 '19 at 19:56

score 2 · Answer 3 · answered Nov 08 '19 at 15:30

2

read about collections.Counter

from collections import Counter

list_3 = list((Counter(list_1) & Counter(list_2)).elements())

answered Nov 08 '19 at 15:30

nonamer92

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score 0 · Answer 4 · answered Nov 08 '19 at 17:56

0

Try this:

[common for common in list_1 if common in list_2]

Happy learning...:)

answered Nov 08 '19 at 17:56

Idrisi_Kasim

81
1
2

1

no.. it is easy but you have bug in case: list_1 = ['A', 'B', 'C', 'C', 'C', 'L', 'C'] list_2 = ['C', 'C', 'F', 'A', 'N', 'L', 'C'] new_list will be: ['A', 'C', 'C', 'C', 'L', 'C'] - here 4C but need 3C – Lzhelis Nov 08 '19 at 21:55

Python: How to generate list with items repeating in two lists

4 Answers4