Convert numeric words to numbers

Last Updated : 19 May, 2023

Given a string S, containing numeric words, the task is to convert the given string to the actual number.

Example:

Input: S = “zero four zero one”
Output: 0401

Input: S = “four zero one four”
Output: 4014

Method #1: Using loop + join() + split()

One of the ways to solve this problem is to use a map, where one can map the numeric with words and then split the strings and rejoin using mapping to numbers.

Python3

# Python3 code to demonstrate working of
# Convert numeric words to numbers
# Using join() + split()
 
help_dict = {
    'one': '1',
    'two': '2',
    'three': '3',
    'four': '4',
    'five': '5',
    'six': '6',
    'seven': '7',
    'eight': '8',
    'nine': '9',
    'zero': '0'
}
 
# initializing string
test_str = "zero four zero one"
 
# printing original string
print("The original string is : " + test_str)
 
# Convert numeric words to numbers
# Using join() + split()
res = ''.join(help_dict[ele] for ele in test_str.split())
 
# printing result
print("The string after performing replace : " + res)

Output

The original string is : zero four zero one
The string after performing replace : 0401

Time complexity: O(n)
Auxiliary space: O(n), where n is length of string.

Method #2: Using word2number library

This problem can also be solved using PyPI library word2number. It has inbuilt functions that convert words to numbers.

Python3

# Python3 code to demonstrate working of
# Convert numeric words to numbers
# Using word2number
from word2number import w2n
 
# initializing string
test_str = "zero four zero one"
 
# printing original string
print("The original string is : " + test_str)
 
# Convert numeric words to numbers
# Using word2number
res = w2n.word_to_num(test_str)
 
# printing result
print("The string after performing replace : " + str(res))

Time complexity: O(n)
Auxiliary space: O(n)

Approach 2: Using Regular Expressions (re)

We can use the re module in Python to find all the word occurrences in the string and then use a dictionary to map the words to numbers. After that, we can use the re.sub function to replace all the word occurrences with their corresponding numbers.

Python3

import re
 
def convert_to_numbers(s):
   
    words_to_numbers = {
        'one': '1',
        'two': '2',
        'three': '3',
        'four': '4',
        'five': '5',
        'six': '6',
        'seven': '7',
        'eight': '8',
        'nine': '9',
        'zero': '0'
    }
 
    pattern = re.compile(r'\b(' + '|'.join(words_to_numbers.keys()) + r')\b')
    return re.sub(pattern, lambda x: words_to_numbers[x.group()], s)
 
 
# Example usage:
s = "zero four zero one"
print(convert_to_numbers(s))

Output

0 4 0 1

Time complexity: O(n)
Auxiliary space: O(n)

Method 4: Using dictionary

Steps:

Split the input string into words using the split() method, and store the resulting list of words in variable words.
We use a list comprehension to map each word in the list words to its corresponding digit using the word_to_digit dictionary and store the resulting list of digits in variable digits.
Join the list of digits into a string using the join() method, and store the resulting string in a variable result.
Print the original string and the result.

Python3

# Define a dictionary that maps
# numeric words to their corresponding digits
word_to_digit = {
    'zero': '0',
    'one': '1',
    'two': '2',
    'three': '3',
    'four': '4',
    'five': '5',
    'six': '6',
    'seven': '7',
    'eight': '8',
    'nine': '9'
}
 
# Initializing string
test_str = 'zero four zero one'
 
# Split the input string into words
words = test_str.split()
 
# Map each word to its corresponding digit using the dictionary
digits = [word_to_digit[word] for word in words]
 
# Join the resulting list of digits into a string
result = ''.join(digits)
 
# Print the original string and the result
print('The original string is:', test_str)
print('The string after performing replace:', result)

Output

The original string is: zero four zero one
The string after performing replace: 0401

Time complexity: O(n), where n is the length of the input string test_str, because we need to traverse the string once to split it into words and once more to map each word to its corresponding digit.
Auxiliary space: O(1), because we only need to store the dictionary, the list of words, the list of digits, and the resulting string, which do not depend on the size of the input.

Method 5: Using list comprehension

This approach uses a list comprehension to iterate through the words in the input string and convert each word to its corresponding digit using a series of if/else statements. The resulting digits are concatenated to form the output string.

Steps:

Split the input string into individual words using list comprehension, iterate through the words in the string, and convert each word to its corresponding digit using if/else statements.
Concatenate the resulting digits to form the output string.
Print the output string.

Python3

original_string = 'zero four zero one'
 
result = ''.join(['0' if word == 'zero' else '1' if word == 'one' else '2' if word == 'two' else '3' if word == 'three' else '4' if word == 'four' else '5' if word == 'five' else '6' if word == 'six' else '7' if word == 'seven' else '8' if word == 'eight' else '9' for word in original_string.split()])
 
print(result)

Output

Time complexity: O(n), where n is the number of words in the input string.
Auxiliary Space: O(n), where n is the number of words in the input string.

Method 6: Using a list of tuples

Python3

# Define a list of tuples that maps numeric words
# to their corresponding digits
word_digit_pairs = [
    ('zero', '0'),
    ('one', '1'),
    ('two', '2'),
    ('three', '3'),
    ('four', '4'),
    ('five', '5'),
    ('six', '6'),
    ('seven', '7'),
    ('eight', '8'),
    ('nine', '9')
]
 
# Define the input string
test_str = 'zero four zero one'
 
# Iterate over each word-digit pair and replacing
# the words with digits in the input string
for word, digit in word_digit_pairs:
    test_str = test_str.replace(word, digit)
 
# Print the original string and the result
print('The original string is:', test_str)

Output

The original string is: 0 4 0 1

Time complexity: O(K) where K is the length of the input string and the number of word-digit pairs in the list.
Auxiliary space: O(1) since we are not using any additional data structures that scale with the input size.