Frequency of Numbers in String - Python

We are given a string and we have to determine how many numeric characters (digits) are present in the given string. For example: "Hello123World456" has 6 numeric characters (1, 2, 3, 4, 5, 6).

Using re.findall()

re.findall() function from the re module is a powerful tool that can be used to match specific patterns in a string. In this case, we use it to find all numeric sequences in the string and count them.

import re
s = "geeks4feeks is No. 1 4 geeks"
# Count numerics in `s`
res = len(re.findall(r'\d+', s))
print(res)

3

Explanation:

• re.findall(r'\d+', test_str) finds all sequences of digits in the string using the regular expression r'\d+' and returns them as a list.
• len() function is then used to count the number of numeric sequences in the list returned by re.findall().

Using sum() and findall()

This method also uses re.findall() but instead of using len() to count the sequences, it uses sum() with re.finditer(). The re.finditer() function returns an iterator of match objects, and we can sum 1 for each match to count the number of numeric sequences.

import re
s = "geeks4feeks is No. 1 4 geeks"
# count number occurrences in `s`
res = sum(1 for _ in re.finditer(r'\d+', s))
print(res)

3

Explanation:

• re.finditer(r'\d+', test_str) return an iterator yielding match objects for each numeric sequence.
• sum(1 for _ in re.finditer(...)), this whole expression sum 1 for each match object and hence effectively counts the number of numeric sequences.

Using map

In this approach, we use the map() function to apply the isdigit() method to each character in the string. The isdigit() method checks whether a character is a numeric digit, and map() returns a map object with True for digits and False otherwise.

s = "geeks4feeks is No. 1 4 geeks"
# count digits in the string
res = sum(map(str.isdigit, s))
print(res)

3

Explanation:

• map(str.isdigit, test_str) applies the isdigit() method to each character in the string, returning True for digits and False otherwise
• sum() function is then used to count the number of True values, which corresponds to the number of digits.

Using isdigit() method

This method involves manually iterating over each character in the string and using the isdigit() method to check if it’s a digit. If a character is a digit, the counter is incremented.

s = "geeks4feeks is No. 1 4 geeks"
res = 0
for i in s:
    if i.isdigit(): res += 1  # count digits
print(res)

3

Explanation: Loop through string s and check each character, and if it's a digit (isdigit()), increment the counter res.

Without using any built-in methods

This method iterates through each character in the given string and checks if it belongs to the set of digits ('0' to '9') without using any built-in methods.

s = "geeks4feeks is No. 1 4 geeks"
# count digits in the string
res = 0
digits = "0123456789"
for i in s:
    if i in digits: res += 1  # increment if character is a digit
print(res)

3

Explanation: We create a string 'digits' and then iterate over the given string s. If the character in s is present in the 'digits' string that we created, we simply increase the counter "res".