Python | Merge adjacent Digit characters

Sometimes, more than one type of data can come in python list and sometimes its undesirably tokenized and hence we require to join the digits that has been tokenized and leave the alphabets as they are. Let’s discuss certain ways in which this task can be achieved. 

Method #1 : Using list comprehension + “*” operator This task can be performed using the list comprehension, first by joining the digits and then joining the words and then separating only the words, while joining to form resultant string. 

Python3

# Python3 code to demonstrate
# Merge adjacent Digit characters
# list comprehension + "*" operator

# initializing list
test_list = ['Geeks', 'for', 'Geeks', '2', '5']

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

# using list comprehension + "*" operator
# Merge adjacent Digit characters
res = [''.join([i for i in test_list if not i.isalpha()]), *[j for j in test_list if j.isalpha()]]

# print result
print("The joined adjacent word list(ignoring alphabets) : " + str(res))

Output : 

The original list : ['Geeks', 'for', 'Geeks', '2', '5']
The joined adjacent word list(ignoring alphabets) : ['25', 'Geeks', 'for', 'Geeks']

Time Complexity: O(n), where n is the length of the input list. This is because we’re using the list comprehension + “*” operator which has a time complexity of O(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 #2 : Using itertools.chain.from_iterable() + groupby() + join() This task can also be performed using the groupby function which groups the alphabets together and then from_iterables function joins the list and characters together joined by the join function. 

Python3

# Python3 code to demonstrate
# Merge adjacent Digit characters
# itertools.chain.from_iterable() + groupby() + join()
from itertools import chain, groupby

# initializing list
test_list = ['Geeks', 'for', 'Geeks', '2', '5']

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

# using itertools.chain.from_iterable() + groupby() + join()
# Merge adjacent Digit characters
num_group = groupby(test_list, key = str.isdigit)
both_group = [[''.join(i)] if j else list(i) for j, i in num_group]
res = list(chain.from_iterable(both_group))

# print result
print("The joined adjacent word list(ignoring alphabets) : " + str(res))

Output : 

The original list : ['Geeks', 'for', 'Geeks', '2', '5']
The joined adjacent word list(ignoring alphabets) : ['25', 'Geeks', 'for', 'Geeks']

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