Python – Incremental Sublist Sum

Sometimes we need to group elements and grouping techniques and requirements vary accordingly. One such way to group the elements is by the i’th size in list which stores the dictionary of index keys with values of summation of subsequent size i. Let’s discuss certain ways in which this can be done. 

Method #1 : Using islice() + sum() + dictionary comprehension The slice method can be used to group the chunks of list required to be made as values of the dictionaries which are then assigned to their destined index key using the dictionary comprehension. The sum() is used to perform sum of created list. 

The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14, 5]
The Incremental Sublist Sum is : {1: 4, 2: 15, 3: 37, 4: 49}

Time complexity: O(n^2) because it uses a nested loop to iterate over all possible sublists.

Auxiliary space: O(n^2) because it creates a dictionary res that potentially stores all possible sublists of the input list test_list.

  Method #2 : Using itemgetter() + takewhile() + islice() + sum() In order to increase the computation speed, we introduce new functions to perform this particular task, takewhile and itemgetter functions which performs the task of grouping the sliced values. The sum() is used to perform sum of created list. 

The original list : [4, 7, 8, 10, 12, 15, 13, 17, 14, 5]
The Incremental Sublist Sum is : {1: 4, 2: 15, 3: 37, 4: 49}

Time complexity: O(n^2) because it uses a nested loop to iterate over all possible sublists.

Auxiliary space: O(n^2) because it creates a dictionary res that potentially stores all possible sublists of the input list test_list.