Python – Extract Strings with a digit

Given a Strings List, extract those with atleast one digit.

Input : test_list = [‘gf4g’, ‘is’, ‘best’, ‘gee1ks’] 
Output : [‘gf4g’, ‘gee1ks’] 
Explanation : 4, 1 are respective digits in string.

Input : test_list = [‘gf4g’, ‘is’, ‘best’, ‘geeks’] 
Output : [‘gf4g’] 
Explanation : 4 is digit in string. 

Method #1 : Using list comprehension + any() + isdigit()

In this iteration for each string is done using list comprehension, any() and isdigit() is used for task of checking at least one digit.

step by step approach:

1. Initialize the input list test_list with some string values.
2. Print the original list.
3. Create a list comprehension using sub as the loop variable to iterate over each element sub in test_list.
4. For each element sub in test_list, use the any() function to check if any character in the string is a digit using the isdigit() method.
5. If the above condition is true, append the element sub to the result list res.
6. Print the list of strings with digits.

Python3

# Python3 code to demonstrate working of
# Extract Strings with a digit
# Using list comprehension + any() + isdigit()

# initializing list
test_list = ['gf4g', 'is', 'best', '4', 'gee1ks']

# printing original list
print("The original list is : " + str(test_list))

# checking if string contain any string using any()
res = [sub for sub in test_list if any(ele for ele in sub if ele.isdigit())]

# printing result
print("Strings with any digit : " + str(res))

Output

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n²)
Space Complexity: O(n)

Method #2 : Using any() + filter() + lambda

In this, we perform task of filtering using lambda and filter(), rest remains the same.

Python3

# Python3 code to demonstrate working of
# Extract Strings with a digit
# Using any() + filter() + lambda

# initializing list
test_list = ['gf4g', 'is', 'best', '4', 'gee1ks']

# printing original list
print("The original list is : " + str(test_list))

# checking if string contain any string using any()
# filter() used to filter strings with digits
res = list(filter(lambda sub: any(
    ele for ele in sub if ele.isdigit()), test_list))

# printing result
print("Strings with any digit : " + str(res))

Output

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n²) 
Space Complexity: O(n)

Method #3 : Without any builtin methods

Python3

# Python3 code to demonstrate working of
# Extract Strings with a digit


def fun(s):
    digits = "0123456789"
    x = s
    for i in digits:
        s = s.replace(i, "")
    if(len(x) != len(s)):
        return True
    return False


# initializing list
test_list = ['gf4g', 'is', 'best', '4', 'gee1ks']

# printing original list
print("The original list is : " + str(test_list))
res = []
for i in test_list:
    if fun(i):
        res.append(i)

# printing result
print("Strings with any digit : " + str(res))

Output

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n*n) where n is the number of elements in the list “test_list”. 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list “test_list”. 

Method #4 : Using ord() function

Python3

# Python3 code to demonstrate working of
# Extract Strings with a digit


# initializing list
test_list = ['gf4g', 'is', 'best', '4', 'gee1ks']

# printing original list
print("The original list is : " + str(test_list))
res = []
for i in test_list:
    for j in i:
        if(ord(j) >= ord('0') and ord(j) <= ord('9')):
            res.append(i)
            break
# printing result
print("Strings with any digit : " + str(res))

Output

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(N*M)

Auxiliary Space: O(1)

Method 5 : Using regular expressions
In this approach, we use the re.search() function from the re module which searches for a pattern in the given string. The pattern ‘\d’ represents a digit in the string. The function returns a match object if there is a match and None otherwise. Hence, for every string in the list, we check if there is a digit present by calling re.search(‘\d’, i) where i is the current string in the list. If there is a match, we add the string i to the resultant list. Finally, the resultant list is returned which has all the strings containing at least one digit.

Python3

import re

#initializing list
test_list = ['gf4g', 'is', 'best', '4', 'gee1ks']

#printing original list
print("The original list is : " + str(test_list))

#using re.search() to search for pattern '\d'
#which represents a digit in the string
res = [i for i in test_list if re.search('\d', i)]

#printing result
print("Strings with any digit : " + str(res))

Output

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n)
Auxiliary Space: O(n)