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Python | Variable list slicing

  • Last Updated : 27 Mar, 2019

The problem of slicing a list has been dealt earlier, but sometimes we need to perform the slicing in variable lengths 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() + list comprehension
The list comprehension can be used to iterate through the list and the component issue is solved using the islice function.




# Python3 code to demonstrate
# variable length slicing
# using itertools.islice() + 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() + list comprehension
# variable length slicing
temp = iter(test_list)
res = [list(islice(temp, part)) for part in slice_list]
  
# print result
print("The variable sliced 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 list is : [[1, 5], [3], [7, 8, 10], [11, 16, 9, 12]]

 

Method #2 : Using zip() + accumulate() + 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.






# Python3 code to demonstrate
# variable length slicing
# using zip() + accumulate() + 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() + list slicing
# variable length slicing
res = [test_list[i - j: i] for i, j in zip(accumulate(slice_list), slice_list)]
  
# print result
print("The variable sliced 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 list is : [[1, 5], [3], [7, 8, 10], [11, 16, 9, 12]]

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