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Python program to convert a list into a list of lists using a step value

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  • Last Updated : 02 Feb, 2021

Given a List, the task here is to write a python program that can split the list into list of lists using by a step value here denoted via K.

Input : test_list = [5, 6, 3, 2, 7, 1, 9, 10, 8], K = 3

Output : [[5, 2, 9], [6, 7, 10], [3, 1, 8]]

Explanation : 5, 2 and 9 are 0th, 3rd and 6th element respectively, and hence ( difference 3 ) grouped together.

Input : test_list = [5, 6, 3, 2, 7, 1], K = 3

Output : [[5, 2], [6, 7], [3, 1]]

Explanation : 5 and 2 are 0th and 3rd element respectively, and hence ( difference 3 ) grouped together.

Method 1 : Using loop and slicing

In this, loop is employed to skip numbers as required, and each subsequent skipped sliced list is extracted using slicing and is appended to result.

Example:

Python3




# initializing list
test_list = [5, 6, 3, 2, 7, 1, 9, 10, 8]
  
# printing original list
print("The original list is : " + str(test_list))
  
# initializing skips
K = 3
  
res = []
for idx in range(0, K):
  
    # 3rd arg. of slicing skips by K
    res.append(test_list[idx::K])
  
# printing result
print("Stepped splitted List : " + str(res))

Output:

The original list is : [5, 6, 3, 2, 7, 1, 9, 10, 8]

Stepped splitted List : [[5, 2, 9], [6, 7, 10], [3, 1, 8]]

Method 2 : Using list comprehension and slicing

Similar to above method, only difference being usage of list comprehension for task of iteration instead of loop for shorthand alternative.

Example:

Python3




# initializing list
test_list = [5, 6, 3, 2, 7, 1, 9, 10, 8]
  
# printing original list
print("The original list is : " + str(test_list))
  
# initializing skips
K = 3
  
# list comprehension used as one liner
res = [test_list[idx::K] for idx in range(0, K)]
  
# printing result
print("Stepped splitted List : " + str(res))

Output:

The original list is : [5, 6, 3, 2, 7, 1, 9, 10, 8]

Stepped splitted List : [[5, 2, 9], [6, 7, 10], [3, 1, 8]]


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