CODEWITHSUNDEEP
pythonduplicates
myname
myname

Reputation: 1347

Keep duplicates in a list in Python

I know this is probably an easy answer but I can't figure it out. What is the best way in Python to keep the duplicates in a list:

x = [1,2,2,2,3,4,5,6,6,7]

The output should be:

[2,6]

I found this link: Find (and keep) duplicates of sublist in python, but I'm still relatively new to Python and I can't get it to work for a simple list.

Upvotes: 9

Views: 12220

Answers (5)

Ivan
Ivan

Reputation: 63

List Comprehension in combination with set() will do exactly what you want.

>>> list(set([i for i in x if x.count(i) > 1]))

[2, 6]

Upvotes: 3

L Ken
L Ken

Reputation: 9

Not efficient but just to get the output, you could try:

import numpy as np

def check_for_repeat(check_list):
    repeated_list = []

    for idx in range(len(check_list)):
        elem = check_list[idx]
        check_list[idx] = None

        if elem in temp_list:
            repeated_list.append(elem)

    repeated_list = np.array(repeated_list)

    return list(np.unique(repeated_list))

Upvotes: 0

mgilson
mgilson

Reputation: 310167

I'd use a collections.Counter:

from collections import Counter
x = [1, 2, 2, 2, 3, 4, 5, 6, 6, 7]
counts = Counter(x)
output = [value for value, count in counts.items() if count > 1]

Here's another version which keeps the order of when the item was first duplicated that only assumes that the sequence passed in contains hashable items and it will work back to when set or yeild was introduced to the language (whenever that was).

def keep_dupes(iterable):
    seen = set()
    dupes = set()
    for x in iterable:
        if x in seen and x not in dupes:
            yield x
            dupes.add(x)
        else:
            seen.add(x)

print list(keep_dupes([1,2,2,2,3,4,5,6,6,7]))

Upvotes: 16

luchosrock
luchosrock

Reputation: 708

keepin' it simple:

array2 = []
aux = 0
aux2=0
for i in x:
    aux2 = i
    if(aux2==aux):
        array2.append(i)
    aux= i
list(set(array2))

That should work

Upvotes: 0

Jochen Ritzel
Jochen Ritzel

Reputation: 107736

This is a short way to do it if the list is sorted already:

x = [1,2,2,2,3,4,5,6,6,7]

from itertools import groupby
print [key for key,group in groupby(x) if len(list(group)) > 1]

Upvotes: 10

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