Python – Sublist Maximum in custom sliced List

Sometimes, while working with data, we can have a problem in which we need to extract maximum not of whole list but of certain customly broken sublists. This kind of problem is peculiar and occurs in many domains. Let’s discuss certain ways in which in which this task can be performed.

Method #1 : Using itertools.islice() + max() + list comprehension
The combination of above methods can be used to solve this problem. In this islice() is used to perform custom slicing and list comprehension is used to iterate and max() is used to compute maximum.

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# Python3 code to demonstrate
# Sublist Maximum in custom sliced List
# 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
# Sublist Maximum in custom sliced List
temp = iter(test_list)
res = [max(list(islice(temp, part))) for part in slice_list]
  
# print result
print("The variable sliced list maximum is : " + str(res))

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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 maximum is : [5, 3, 10, 16]

 

Method #2 : Using zip() + accumulate() + max() + 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. The max() is used to perform maximum.

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# Python3 code to demonstrate
# Sublist Maximum in custom sliced List
# using zip() + accumulate() + list slicing + max()
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 + max()
# Sublist Maximum in custom sliced List
res = [max(test_list[i - j: i]) for i, j in zip(accumulate(slice_list), slice_list)]
  
# print result
print("The variable sliced list maximum is : " + str(res))

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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 maximum is : [5, 3, 10, 16]



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