Use Counter to count unique values in multiple lists

I have a list of lists and I’m trying to use Counter to get the number of unique words across all of the lists.

[[‘My’,
‘name’,
 ‘is’,
 ‘Joe’],
[‘My’,
 ‘name’,
 ‘is’,
 ‘Sally’],
[‘My’,
 ‘name’,
 ‘is’,
 ‘Mike’]]

If it were just the first list I think I could do this:

counter_object = Counter(my_list[0])
keys = counter_object.keys()
num_values = len(keys)

print(num_values)

But unsure about doing this for multiple. Any help is much appreciated, thanks.

Edit: The expected output is 6. Because unique words ‘My’,
‘name’, ‘is’, ‘Joe’, ‘Sally’, ‘Mike’ total to 6.

>Solution :

If I understand your question correctly, you want to count the unique items from each sublists.

# MM = is your list
from collections import Counter   

def count_unique(M):
    flats = [x for sub in M for x in sub]
   
    counts = Counter(flats)

    return len(counts.keys())



print(count_unique(MM))     # check it 
# 6