Comparing Python nested lists and count duplicates

Question

I have two nested lists with strings (list_a and list_b), details below:

list_a = [
('shop1', 'stand1', 'shelf1', 'fruit1'),
('shop1', 'stand1', 'shelf2', 'fruit2'),
('shop1', 'stand1', 'shelf3', 'fruit3'),
('shop1', 'stand2', 'shelf1', 'fruit1'),
('shop1', 'stand2', 'shelf2', 'fruit2'),
('shop1', 'stand2', 'shelf3', 'fruit3'),
('shop2', 'stand3', 'shelf1', 'fruit1'),
('shop2', 'stand3', 'shelf2', 'fruit2'),
('shop2', 'stand3', 'shelf3', 'fruit3')
]
list_b = [
('shop1', 'stand1', 'shelf1', 'fruit1'),
('shop1', 'stand1', 'shelf2', 'fruit2'),
('shop1', 'stand1', 'shelf2', 'fruit2'),
('shop1', 'stand1', 'shelf3', 'fruit3'),
('shop1', 'stand1', 'shelf3', 'fruit3'),
('shop1', 'stand1', 'shelf3', 'fruit3'),
('shop1', 'stand2', 'shelf1', 'fruit1'),
('shop1', 'stand2', 'shelf1', 'fruit1'),
('shop1', 'stand2', 'shelf1', 'fruit1'),
('shop1', 'stand2', 'shelf2', 'fruit2'),
('shop1', 'stand2', 'shelf2', 'fruit2'),
('shop1', 'stand2', 'shelf2', 'fruit2'),
('shop1', 'stand2', 'shelf3', 'fruit3'),
('shop2', 'stand3', 'shelf1', 'fruit1'),
('shop2', 'stand3', 'shelf1', 'fruit1'),
('shop2', 'stand3', 'shelf2', 'fruit2'),
('shop2', 'stand3', 'shelf3', 'fruit3'),
('shop2', 'stand3', 'shelf3', 'fruit3'),
('shop2', 'stand3', 'shelf3', 'fruit3')
]

and I would like to find identical rows from list_b in list_a, count "duplicated" rows and merge list_a with one additional column (number of occurrences) as a new list, like this below:

result_list = [
('shop1', 'stand1', 'shelf1', 'fruit1', 1),
('shop1', 'stand1', 'shelf2', 'fruit2', 2),
('shop1', 'stand1', 'shelf3', 'fruit3', 3),
('shop1', 'stand2', 'shelf1', 'fruit1', 3),
('shop1', 'stand2', 'shelf2', 'fruit2', 3),
('shop1', 'stand2', 'shelf3', 'fruit3', 1),
('shop2', 'stand3', 'shelf1', 'fruit1', 2),
('shop2', 'stand3', 'shelf2', 'fruit2', 1),
('shop2', 'stand3', 'shelf3', 'fruit3', 3)
]

Is there any quick and efficient way to do this?

Possible duplicate of - http://stackoverflow.com/questions/642763/python-intersection-of-two-lists or http://stackoverflow.com/questions/2029795/comparing-python-nested-lists — Rohit Jain, Sep 25 '12 at 17:58
WEll, didn't noticed that you want frequency also.. Then those links doesn't contain what you want.. — Rohit Jain, Sep 25 '12 at 18:03

Andrew Clark · Accepted Answer · 2012-09-25T20:21:42.183

2

dict_a = {row: 0 for row in list_a}
for row in list_b:
    if row in dict_a:
        dict_a[row] += 1

result = [row + (dict_a[row],) for row in list_a]

On Python 2.6 use dict((row, 0) for row in list_a) instead of the dictionary comprehension.

edited Sep 25 '12 at 20:21

answered Sep 25 '12 at 18:03

Andrew Clark

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Works beautiful but I forgot to mention about version of my Python, it's 2.6, so I've changed it a bit. Thank You very much! – jusef Sep 25 '12 at 18:56

score 1 · Answer 2 · answered Sep 25 '12 at 18:02

1

using Counter():

    >>> from collections import Counter
    >>> count=Counter(list_b)
    >>> [list(x)+[count[x]] for x in list_a]

    [['shop1', 'stand1', 'shelf1', 'fruit1', 1], 
    ['shop1', 'stand1', 'shelf2', 'fruit2', 2],
    ['shop1', 'stand1', 'shelf3', 'fruit3', 3],
    ['shop1', 'stand2', 'shelf1', 'fruit1', 3],
    ['shop1', 'stand2', 'shelf2', 'fruit2', 3],
    ['shop1', 'stand2', 'shelf3', 'fruit3', 1],
    ['shop2', 'stand3', 'shelf1', 'fruit1', 2], 
    ['shop2', 'stand3', 'shelf2', 'fruit2', 1], 
    ['shop2', 'stand3', 'shelf3', 'fruit3', 3]]`

answered Sep 25 '12 at 18:02

Ashwini Chaudhary

244,495
58
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Works beautiful but I forgot to mention about version of my Python, it's 2.6, so I've changed it a bit. Thank You very much! – jusef Sep 25 '12 at 18:54
you can use `defaultdict` in pythom 2.6. – Ashwini Chaudhary Sep 25 '12 at 19:05

score 0 · Answer 3 · edited May 23 '17 at 10:24

0

These are not nested lists but tuples. Which is actually your saving. See Most Efficient way to calculate Frequency of values in a Python list? which should work almost right away. To get the duplicates, take keys() of both dictionaries, and calculate their difference.

edited May 23 '17 at 10:24

Community

1
1

answered Sep 25 '12 at 17:59

Antti Haapala -- Слава Україні

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Works beautiful from Your link. Thank You very much! – jusef Sep 25 '12 at 18:57

Comparing Python nested lists and count duplicates

3 Answers3