Python program to extract numeric suffix from string

Given a string of characters with digits embedded in it. The task is to write a Python program to extract all the numbers that are trailing, i.e at the suffix of the string. 

Examples:

Input : test_str = "GFG04"
Output : 04
Explanation : 04 is suffix of string and number hence extracted.

Input : test_str = "GFG143"
Output : 143
Explanation : 143 is suffix of string and number hence extracted.

Method #1 : Using loop + isdigit() + slicing 

In this, the string is reversed using slicing, and occurrence of 1st non-digit element is recorded using isdigit, and at last, list is sliced till the element and reversed again to get the suffix number.

# Python3 code to demonstrate working of
# Extract Suffix numbers
# Using loop + isdigit() + slicing 

# initializing string
test_str = "GFG04"

# printing original string
print("The original string is : " + str(test_str))

# loop for fetching the 1st non digit index 
rev_str = test_str[::-1] 
temp_idx = 0

for idx, ele in enumerate(rev_str):
    if not ele.isdigit():
        temp_idx = idx
        break

# reversing the extracted string to
# get number 
res = rev_str[:temp_idx][::-1]
        
# printing result
print("Suffix number : " + str(res))

The original string is : GFG04
Suffix number : 04

Method #2: Using regex

Appropriate regex can be employed to solve this problem. Provides a compact solution to the problem.

# Python3 code to demonstrate working of
# Extract Suffix numbers
# Using regex
import re

# initializing string
test_str = "GFG04"

# printing original string
print("The original string is : " + str(test_str))

# regex to extract number 
res = re.search(r"(\d+)$", test_str).group()
        
# printing result
print("Suffix number : " + str(res))

The original string is : GFG04
Suffix number : 04

The time and space complexity for all the methods are the same:

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

Method #3: Without isdigit() method

# Python3 code to demonstrate working of
# Extract Suffix numbers

# initializing string
test_str = "GFG04"

# printing original string
print("The original string is : " + str(test_str))

# loop for fetching the 1st non digit index 
rev_str = test_str[::-1] 
temp = 0
digits = "0123456789"
for i, ele in enumerate(rev_str):
    if not ele in digits:
        temp = i
        break

# reversing the extracted string to
# get number 
res = rev_str[:temp][::-1]
        
# printing result
print("Suffix number : " + str(res))

The original string is : GFG04
Suffix number : 04

Method#4: Using list comprehension

test_str = "GFG04"

# Printing original string
print("The original string is : " + str(test_str))

# Using list comprehension to extract suffix number
res = ''.join([char for char in test_str[::-1] if char.isdigit()])[::-1]

# Printing result
print("Suffix number : " + str(res))
#This code is contributed by Vinay Pinjala.

The original string is : GFG04
Suffix number : 04

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

Method#5: Using filter and join method.

# Python3 code to demonstrate working of
# Extract Suffix numbers
# Using filter method


# initializing string
test_str = "GFG04"

# printing original string
print("The original string is : " + str(test_str))


res = ''.join(filter(str.isdigit, test_str[::-1]))[::-1]
        
# printing result
print("Suffix number : " + str(res))
#this code contributed by tvsk

The original string is : GFG04
Suffix number : 04

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

Method#6: Using rfind() and string slicing

Step by step Algorithm:

1. Find the index of the first non-digit character in the string using a lambda function and filter.
2. Find the last occurrence of this non-digit character using rfind() function.
3. Extract the suffix number using string slicing from the index of the non-digit character to the end of the string.
4. Print the suffix number.

test_str = "GFG04"

# printing original string
print("The original string is : " + str(test_str))

# using rfind() and string slicing to extract suffix numbers
temp_idx = test_str.rfind(next(filter(lambda x: not x.isdigit(), test_str[::-1])))

res = test_str[temp_idx+1:]

# printing result
print("Suffix number : " + str(res))

The original string is : GFG04
Suffix number : 04

Time Complexity: O(n), where n is the length of the string. The lambda function and filter takes O(n) time, while rfind() and string slicing takes constant time.
Space Complexity: O(1), as we are not using any extra space.

Method #7: Using rpartition() + isdigit()

• Initialize the string
• Use the rpartition() method to split the string into 3 parts - the part before the last digit, the last digit, and the part after the last digit.
• Check if the last part (the part after the last digit) is empty, which indicates that the last character was a digit.
• If the last part is not empty, there was no numeric suffix in the original string, so print an appropriate message.
• If the last part is empty, check if the middle part (the last digit) is a digit.
• If the middle part is not a digit, there was no numeric suffix in the original string, so print an appropriate message.
• If the middle part is a digit, print it as the numeric suffix.

# initializing string
test_str = "GFG04"

# printing original string
print("The original string is : " + str(test_str))

# extracting suffix number
res = test_str.rpartition('GFG')[2]

# checking if suffix is numeric
if res.isdigit():
   # printing suffix number
   print("Suffix number : " + str(res))
else:
   # printing error message
   print("No suffix number found in string!")

The original string is : GFG04
Suffix number : 04

Time Complexity: O(n), where n is the length of the string. 
Auxiliary Space: O(n), as we are creating a new string to store the extracted suffix.

Method #8: Using numpy:

1. Initialize the input string.
2. Convert the string to a NumPy array of characters.
3. Convert the array to a string using NumPy's char module.
4. Find the indices of all the numeric characters in the string using the where() method from NumPy.
5. Extract the suffix numbers by joining the characters at the found indices.
6. Print the extracted suffix numbers.
    

import numpy as np

# initializing string
test_str = "GFG04"
# printing original string
print("The original string is : " + str(test_str))
# convert string to numpy array of characters
char_array = np.array(list(test_str))

# convert array to string using numpy's char module
char_string = np.char.mod('%c', char_array)

# find indices of all numeric characters
indices = np.where(np.char.isdigit(char_string))[0]

# extract suffix numbers
suffix_numbers = ''.join(char_array[indices])

# print result
print("Suffix number: " + suffix_numbers)
#This code is contributed by Jyothi pinjala.

Output:
The original string is : GFG04
Suffix number: 04

Time complexity:

The list() function in Python has a time complexity of O(n), where n is the length of the string. This operation is done once in our code.
The np.array() function in NumPy also has a time complexity of O(n), where n is the length of the string. This operation is also done once in our code.
The np.char.mod() function in NumPy has a time complexity of O(n), where n is the length of the string. This operation is also done once in our code.
The np.where() function in NumPy has a time complexity of O(n), where n is the length of the string. This operation is done once in our code.
The join() function in Python has a time complexity of O(n), where n is the length of the extracted suffix numbers. This operation is done once in our code.

Auxiliary Space:

The space complexity of our code depends on the length of the string. The input string is stored once as a string variable and then converted to a NumPy array, which also takes up space in memory. The space complexity is O(n), where n is the length of the string.

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