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Python | List Initialization with alternate 0s and 1s

  • Last Updated : 07 Feb, 2019

The initialization of list with a single number is a generic problem whose solution has been dealt many number of times. But sometimes we require to initialize the list with elements alternatively repeating K no. of times. This has use cases in M.L or A.I algorithms which require presetting of data in lists. Let’s discuss certain ways in which this problem is solved.

Method #1 : Using list comprehension
In this method, we insert elements in the list alternatively for the specific number of times of each elements’ occurrence. It takes the remainder of sum of counts of both occurrences of elements with particular occurrence of element for cycle computation.

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# Python3 code to demonstrate 
# to perform cyclic initialization
# using list comprehension
  
# count of 1 
count_1 = 4
  
# count of 0
count_0 = 3
  
# total length of list 
size = 14
  
# initializing list cyclically
# using list comprehension
test_list =  [ 1 if i % (count_1 + count_0) < count_1 
                 else 0 for i in range(size) ]
  
# printing list after change
print ("The list after initializing : " + str(test_list))
Output:
The list after initializing : [1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0]

 
Method #2 : Using itertools.cycle() + itertools.islice()
This is the most pythonic way in which we can perform the cyclic initialization. Slice each of the part of list into the allotted element size in a cyclic manner using cycle function.




# Python3 code to demonstrate 
# to perform cyclic initialization
# using itertools.cycle() + itertools.islice()
import itertools
  
# count of 1 
count_1 = 4
  
# count of 0
count_0 = 3
  
# total length of list 
size = 16
  
# getting pattern
pattern = [1] * count_1 + [0] * count_0
  
# initializing list cyclically
# using itertools.cycle() + itertools.islice()
test_list = list(itertools.islice(itertools.cycle(pattern), size))
  
# printing list after change
print ("The list after initializing : " + str(test_list))
Output:
The list after initializing : [1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 1, 1]



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