Counting the number of different 5 characters substrings inside a string

Question

Given a string i want to count how many substrings with len = 5 i have on it.

For example: Input: "ABCDEFG" Output: 3

And I'm not sure what should be the easiest and fast way to do this in python. Any idea?

Update:

I want only to count different substrings.

Input: "AAAAAA" Substrings: 2 times "AAAAA" Output: 1

Answer 1

>>> n = 5
>>> for s in 'ABCDEF', 'AAAAAA':
...     len({s[i:i+n] for i in range(len(s)-n+1)})
... 
2
1

Answer 2

To get the sub strings you could use NLTK like this:

>>> from nltk.util import ngrams
>>> for gram in ngrams("ABCDEFG", 5):
...     print gram
... 
('A', 'B', 'C', 'D', 'E')
('B', 'C', 'D', 'E', 'F')
('C', 'D', 'E', 'F', 'G')

You could apply a Counter and then get the unique n-grams (and their frequency) like so:

>>> Counter(ngrams("AAAAAAA", 5))
Counter({('A', 'A', 'A', 'A', 'A'): 3})

Answer 3

Using list comprehension (code golf):

findSubs=lambda s,v:[''.join([s[i+j] for j in range(v)]) for i,x in enumerate(s) if i<=len(s)-v]
findCount=lambda s,v:len(findSubs(s,v))

print findSubs('ABCDEFG', 5)  #returns ['ABCDE', 'BCDEF', 'CDEFG']
print findCount('ABCDEFG', 5) #returns 3

---

Update

For your update, you could cast the list above to a set, back to a list, then sort the strings.

findUnique=lambda s,v:sorted(list(set(findSubs(s,v))))
findUniqueCount=lambda s,v:len(findUnique(s,v))

print findUnique('AAAAAA', 5)      #returns ['AAAAA']
print findUniqueCount('AAAAAA', 5) #returns 1