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I want to count how often a sequence multiple characters occurs in a string. For example, I want to see how many times ad appears in badhadmad. I thought about using a for loop but I don't know how to iterate more than one character. How can I accomplish ths?

Adriaan
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Minh Phúc Nguyễn
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    How about simple `"badhadmad".count('ad')` :)? – Chris Aug 20 '19 at 07:24
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    Possible duplicate of [Count number of occurrences of a given substring in a string](https://stackoverflow.com/questions/8899905/count-number-of-occurrences-of-a-given-substring-in-a-string) – Georgy Aug 20 '19 at 07:35
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    @Chris But `"ababa".count('aba') == 1` :D? – TrebledJ Aug 20 '19 at 07:35
  • @TrebledJ True! `str.count` won't work in such cases. In that case, iteration is indeed one way: `sum(1 for i in range(len("ababa")) if "aba" == s[i:i+len("aba")])`. – Chris Aug 20 '19 at 07:43

3 Answers3

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Use this to count the number of occurrences of a sub-string in python.

s = "badhadmad"

print(s.count("ad"))

Using loop:

s = "badhadadmad"
l = len(s)
pattern = "ad"
n = len(pattern)
count = 0
for i in range(l - n):
  if s[i] == pattern[0]:
    if s[i:i+n] == pattern:
      count += 1
print("Ans",count)

.count() gives only non-overlapping solution, for overlapping sub-strings:

import re
print(len(re.findall('(?=aba)', 'ababa')))
Yash
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    Also, why the double check on the first character? – Tomerikoo Aug 20 '19 at 07:42
  • I'd like to know if it is a major computational redundancy? – Yash Aug 20 '19 at 07:43
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    probably a small one, but in Python readability counts :) Also count on Python to do the check efficiently. I'm sure that by doing `s[i:i+n] == pattern` if the first character doesn't match, no extra computation will be carried out – Tomerikoo Aug 20 '19 at 07:45
  • True that but I think readability is a subjective thing. Some find it redundant what other may find readable and vice versa. – Yash Aug 20 '19 at 07:47
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    Well with that I can't argue obviously :) – Tomerikoo Aug 20 '19 at 07:49
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Just use count method over a string in python

x = "badhadmad"
x.count("ad")
# 3

Go through https://www.programiz.com/python-programming/methods/string/count for more usage of count method

Shrey
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Generate character level n grams for your string str, 

[str[i:i+n] for i in range(len(str)-n+1)]

and then use count if needed. You can loop over range of values of n you want to consider.

Deven
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