Python – Consecutive K elements join in List

Sometimes, while working with Python lists, we can have a problem in which we need to join every K characters into one collection. This type of application can have use case in many domains like day-day and competitive programming. Lets discuss certain ways in which this task can be performed.

Method #1 : Using List comprehension
This is one of the ways by which this task can be performed. In this, we iterate through the list and join elements using list slicing and return the aggregated list.

# Python3 code to demonstrate
# Consecutive K elements join in List
# using List comprehension

# Initializing list
test_list = ['g', 'f', 'g', 'i', 's', 'b', 'e', 's', 't']

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

# Initializing K
K = 3

# Consecutive K elements join in List
# using List comprehension
res = [ "".join(test_list[idx : idx + K]) for idx in range(len(test_list) - K + 1) ]

# printing result
print ("List after consecutive joining : " + str(res))

Output :

The original list is : [‘g’, ‘f’, ‘g’, ‘i’, ‘s’, ‘b’, ‘e’, ‘s’, ‘t’]
List after consecutive joining : [‘gfg’, ‘fgi’, ‘gis’, ‘isb’, ‘sbe’, ‘bes’, ‘est’]

Method #2 : Using loop
This is brute way to perform this task. This is similar to above method, just the string is iterated using a loop and making task more longer and tedious.

# Python3 code to demonstrate
# Consecutive K elements join in List
# using loop

# Initializing list
test_list = ['g', 'f', 'g', 'i', 's', 'b', 'e', 's', 't']

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

# Initializing K
K = 3

# Consecutive K elements join in List
# using loop
res = []
for idx in range(0, len(test_list) - K + 1):
    res.append("".join(test_list[idx : idx + K]))

# printing result
print ("List after consecutive joining : " + str(res))

Output :

The original list is : [‘g’, ‘f’, ‘g’, ‘i’, ‘s’, ‘b’, ‘e’, ‘s’, ‘t’]
List after consecutive joining : [‘gfg’, ‘fgi’, ‘gis’, ‘isb’, ‘sbe’, ‘bes’, ‘est’]