Python | Embedded Numbers Summation in String List

Sometimes, while working with Python lists, we can have problem in which we need to concatenate embedded numbers in Strings list and perform its summation. This can have application in domains dealing with data. Lets discuss certain ways in which this task can be performed. 

Method #1 : Using join() + loop The combination of above functionalities can be used to perform this task. In this, we perform the task of extracting number using join() and loop is used to perform the task of summation. 

Python3

# Python3 code to demonstrate working of
# Embedded Numbers Summation in String List
# Using join() + loop

# initializing list
test_list = ['g4fg', 'i4s5', 'b9e4st']

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

# Embedded Numbers Summation in String List
# Using join() + loop
res = 0
for sub in test_list:
    res += int(''.join(chr for chr in sub if chr.isdigit()))

# printing result
print("The summation of strings : " + str(res))

Output : 

The original list is : ['g4fg', 'i4s5', 'b9e4st']
The summation of strings : 143

Time Complexity: O(n) where n is the total number of values in the list “test_list”. 
Auxiliary Space: O(n) where n is the total number of values in the list “test_list”.

Method #2 : Using sum() + list comprehension The combination of above functions can also be used to perform this task. In this, we perform summation using sum() and list comprehension is used to compile string of numbers for summation to work upon. 

Python3

# Python3 code to demonstrate working of
# Embedded Numbers Summation in String List
# Using sum() + list comprehension

# initializing list
test_list = ['g4fg', 'i4s5', 'b9e4st']

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

# Embedded Numbers Summation in String List
# Using sum() + list comprehension
res = sum([int(''.join(chr for chr in sub if chr.isdigit()))
                                      for sub in test_list])

# printing result
print("The summation of strings : " + str(res))

Output : 

The original list is : ['g4fg', 'i4s5', 'b9e4st']
The summation of strings : 143

Time Complexity: O(n*n), where n is the length of the input list. This is because we’re using the sum() + list comprehension which has a time complexity of O(n*n) in the worst case.
Auxiliary Space: O(n), as we’re using additional space res other than the input list itself with the same size of input list.

Method 3: Using re.findall() and sum()

Python3

import re

#initializing list
test_list = ['g4fg', 'i4s5', 'b9e4st']

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

#Embedded Numbers Summation in String List
#Using re.findall() and sum()
res = sum(int("".join(re.findall(r'\d+', sub))) for sub in test_list )

#printing result
print("The summation of strings : " + str(res))

Output

The original list is : ['g4fg', 'i4s5', 'b9e4st']
The summation of strings : 143

Time complexity: O(n), where n is the total number of characters in all the strings in the list.
Auxiliary Space: O(1), as we are not using any additional data structure to store the extracted numbers.

Explanation: The re.findall() function returns a list of all the occurrences of the given pattern in the input string. In this case, the pattern is ‘\d+’, which matches one or more digits. Then, we use a nested list comprehension to extract all the numbers and finally use the sum() function to sum them up.

Method #4 : Using replace() method and for loops

Approach 

• Initiated a nested for loop
• First loop to traverse list of strings
• Second loop to replace all alphabets in string
• Finally convert numeric character to integer and sum them
• Display the sum

Python3

# Python3 code to demonstrate working of
# Embedded Numbers Summation in String List

# initializing list
test_list = ['g4fg', 'i4s5', 'b9e4st']

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

# Embedded Numbers Summation in String List
la="abcdefghijklmnopqrstuvwxyz"
ua="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
res = 0
for sub in test_list:
    for j in la+ua:
        sub=sub.replace(j,"")
    res+=int(sub)


# printing result
print("The summation of strings : " + str(res))

Output

The original list is : ['g4fg', 'i4s5', 'b9e4st']
The summation of strings : 143

Time Complexity : O(N*N)
Auxiliary Space : O(1)

Method #5: Using map() and sum()

• Define a function to extract digits from a string and convert them to integers.
• Use the map() function to apply the function from step 1 to each element in the list.
• Use the sum() function to calculate the summation of the resulting list of integers.

Python3

# Python3 code to demonstrate working of
# Embedded Numbers Summation in String List
# Using map() and sum()

# initializing list
test_list = ['g4fg', 'i4s5', 'b9e4st']

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

# Define a function to extract digits from a string and convert them to integers
def extract_and_convert(s):
    return int(''.join(filter(str.isdigit, s)))

# Using map() and sum()
res = sum(map(extract_and_convert, test_list))

# printing result
print("The summation of strings: " + str(res))

Output

The original list is: ['g4fg', 'i4s5', 'b9e4st']
The summation of strings: 143

Time Complexity: O(n), where n is the total number of characters in the input list.
Auxiliary Space: O(1), as we only use a constant amount of extra space for variables. 

Method #6: Using reduce() and lambda

In this method, reduce() function is imported from functools module. Then, the input list test_list is initialized. A lambda function is defined to extract digits from a string and convert them to integers. Then, reduce() function is used to apply the lambda function to each element of the input list, with an initial value of 0. The reduce() function accumulates the sum of the integers extracted from each string element and returns the final result. Finally, the result is printed using the print() function.

Python3

# Python3 code to demonstrate working of
# Embedded Numbers Summation in String List
# Using reduce() and lambda

from functools import reduce

# initializing list
test_list = ['g4fg', 'i4s5', 'b9e4st']

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

# Define a lambda function to extract digits from a string and
#convert them to integers
extract_and_convert = lambda s: int(''.join(filter(str.isdigit, s)))

# Using reduce() and lambda
res = reduce(lambda acc, x: acc + extract_and_convert(x), test_list, 0)

# printing result
print("The summation of strings: " + str(res))

The original list is: ['g4fg', 'i4s5', 'b9e4st']
The summation of strings: 143

Time Complexity: O(n), where n is the number of elements in the input list, as both the lambda function and the reduce() function iterate through the list once.
Auxiliary Space: O(1), as we only use a constant amount of extra space for variables.