python - Get a unique list of items that occur more than once in a list

Question

I have a list of items:

mylist = ['A','A','B','C','D','E','D']

I want to return a unique list of items that appear more than once in mylist, so that my desired output would be:

 [A,D]

Not sure how to even being this, but my though process is to first append a count of each item, then remove anything equal to 1. Then dedupe, but this seems like a really roundabout, inefficient way to do it, so I am looking for advice.

Answer 1

You can use collections.Counter to do what you have described easily:

from collections import Counter
mylist = ['A','A','B','C','D','E','D']
cnt = Counter(mylist)
print [k for k, v in cnt.iteritems() if v > 1]
# ['A', 'D']