How do I check if each letter is in multiple strings?

Question

I have an array:

arr = ['ab', 'ac']

I want to check which letters are repeated for all items in arr. For the above, 'a' is in both. I would then want to print '1'.

Another example would be:

arr = ['abc', 'dca', 'ac']

'a' and 'c' are common to all, so I would print 2.

Any idea how to do this?

Answer 1

You can make a set of the letters of each string, and determine the intersection of all sets:

arr = ['abc', 'dca', 'ac']

common = set.intersection(*(set(string) for string in arr))
print(common)
# {'a', 'c'}

print(len(common))
# 2

set.intersection accepts any number of arguments, we use the * to unpack the generator expression yielding the sets.

Answer 2

You can convert your entries into sets, then find their intersection:

arr = ['abc', 'dca', 'ac']

set_list = [set(a) for a in arr]
intersection = set.intersection(*set_list)

print(intersection)
print(len(intersection))

Output:

{'c', 'a'}
2

References:

Answer 3

here i converted the first element of list to to set for using thee intersection and it worked pretty good

list_of_sets=['acb', 'ac']
print(len(set(list_of_sets[0]).intersection(*list_of_sets[1:])))

Answer 4

Using set and reduce could help out here:

from functools import reduce 

print(len(reduce(lambda x,y: set.intersection(set(x),set(y)),arr)))

ouputs