Python | Incremental slice partition in list

Last Updated : 27 Aug, 2019

Sometimes, while working with lists, we can come across a problem in which we need to slice a list incrementally, i.e, with each slice, number of elements increase by 1. This has application in competitive programming. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using loops
This is the brute force method by which this task can be performed. We just manually count and increase the counter with each iteration for slicing and dictionary key creation.

# Python3 code to demonstrate working of
# Incremental slice partition in list
# Using loop
  
# initializing list
test_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  
# printing original list
print("The original list is : " + str(test_list))
  
# Incremental slice partition in list
# Using loop
res = {}
N = 1
strt = 0
while strt < len(test_list):
    res[N] = test_list[strt : strt + N]
    strt += N
    N += 1
  
# printing result 
print("The partitioned dictionary from list is : " + str(res))

Output :

The original list is : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
The partitioned dictionary from list is : {1: [1], 2: [2, 3], 3: [4, 5, 6], 4: [7, 8, 9, 10]}

Method #2 : Using enumerate() + slice() + next() + iter() + count()
The combination of above functions can be used to perform this task. In this, next() is used to iterate the list converted to iterator by iter(). The slice() performs list slicing. The count() helps in managing the counter and enumerate keeps track of element and indices in list.

# Python3 code to demonstrate working of
# Incremental slice partition in list
# Using enumerate() + slice() + next() + iter() + count()
from itertools import islice, count
  
# initializing list
test_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  
# printing original list
print("The original list is : " + str(test_list))
  
# Incremental slice partition in list
# Using enumerate() + slice() + next() + iter() + count()
res = {key : val for key, val in enumerate(iter(lambda i = iter(test_list),
                          c = count(1): list(islice(i, next(c))), []), 1)}
  
# printing result 
print("The partitioned dictionary from list is : " + str(res))

Output :

The original list is : [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
The partitioned dictionary from list is : {1: [1], 2: [2, 3], 3: [4, 5, 6], 4: [7, 8, 9, 10]}

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