How do I get the number of lists with a particular element?

Question

I have a list of lists, which looks like

listOfLists = [
    ['a','b','c','d'],
    ['a','b'],
    ['a','c'],
    ['c','c','c','c']  
 ] 

I want to count the number of lists which have a particular element. For Example, my output should be

{'a':3,'b':2,'c':3,'d':1}

As you can see, I don't need the total count of an element. In the case of "c", though its total count is 5, the output is 3 as it occurs only in 3 lists.

I am using a counter to get the counts. The same can be seen below.

line_count_tags = []
for lists in lists_of_lists:
    s = set()
    for element in lists:
         s.add(t)
    lines_count_tags.append(list(s))

count = Counter([count for counts in lines_count_tags for count in counts])

So, when I print count, I get

{'a':3,'c':3,'b':2,'d':1}

I want to know if there's a much better way to accomplish my goal.

Answer 1

Use a Counter and convert each list to a set. The set will remove any duplicates from each list so that you don't count duplicate values in the same list:

>>> from collections import Counter

>>> Counter(item for lst in listOfLists for item in set(lst))
Counter({'a': 3, 'b': 2, 'c': 3, 'd': 1})

If you like functional programming you can also feed a chain of set-mapped listOfLists to the Counter:

>>> from collections import Counter
>>> from itertools import chain

>>> Counter(chain.from_iterable(map(set, listOfLists)))
Counter({'a': 3, 'b': 2, 'c': 3, 'd': 1})

Which is totally equivalent (except maybe being a bit faster) to the first approach.