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Python | Custom List slicing Sum
  • Last Updated : 18 Feb, 2020

The problem of slicing a list has been dealt earlier, but sometimes we need to perform the slicing in variable lengths and its summation according to the input given in other list. This problem has its potential application in web development. Let’s discuss certain ways in which this can be done.

Method #1 : Using itertools.islice() + sum() + list comprehension
The list comprehension can be used to iterate through the list and the component issue is solved using the islice function. Summation is performed by sum().




# Python3 code to demonstrate
# Custom List slicing Sum
# using itertools.islice() + sum() + list comprehension
from itertools import islice
  
# initializing test list
test_list = [1, 5, 3, 7, 8, 10, 11, 16, 9, 12]
  
# initializing slice list 
slice_list = [2, 1, 3, 4]
  
# printing original list 
print("The original list : " + str(test_list))
  
# printing slice list 
print("The slice list : " + str(slice_list))
  
# using itertools.islice() + sum() + list comprehension
# Custom List slicing Sum
temp = iter(test_list)
res = [sum(list(islice(temp, part))) for part in slice_list]
  
# print result
print("The variable sliced sum list is : " + str(res))
Output :
The original list : [1, 5, 3, 7, 8, 10, 11, 16, 9, 12]
The slice list : [2, 1, 3, 4]
The variable sliced sum list is : [6, 3, 25, 48]

 

Method #2 : Using zip() + accumulate() + sum() + list slicing
Apart from using the list comprehension to perform the task of binding, this method uses zip function to hold sublist element together, accumulate function joins the elements, and slicing is used to construct the required slicing. Summation is performed by sum().






# Python3 code to demonstrate
# Custom List slicing Sum
# using zip() + accumulate() + sum() + list slicing
from itertools import accumulate
  
# initializing test list
test_list = [1, 5, 3, 7, 8, 10, 11, 16, 9, 12]
  
# initializing slice list 
slice_list = [2, 1, 3, 4]
  
# printing original list 
print("The original list : " + str(test_list))
  
# printing slice list 
print("The slice list : " + str(slice_list))
  
# using zip() + accumulate() + sum() + list slicing
# Custom List slicing Sum
res = [sum(test_list[i - j: i]) for i, j in zip(accumulate(slice_list), slice_list)]
  
# print result
print("The variable sliced sum list is : " + str(res))
Output :
The original list : [1, 5, 3, 7, 8, 10, 11, 16, 9, 12]
The slice list : [2, 1, 3, 4]
The variable sliced sum list is : [6, 3, 25, 48]

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