Python | Ways to rotate a list

The rotation of a list has been discussed earlier also, but this particular article focuses on shorthands and various short techniques to achieve this in one-liners or one word. This operation is quite essential in a programmers life to achieve various tasks.

Let’s discuss different ways we can rotate a list.

Method #1 : Using Slicing
This particular method is the generic method and mostly employed to achieve this task and also been discussed in many articles as well. It works by just joining the later sliced part to the initial sliced part given the rotation number.



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# Python3 code to demonstrate 
# rotation of list 
# using slice 
  
# initializing list
test_list = [1, 4, 6, 7, 2]
  
# printing original list 
print ("Original list : " + str(test_list))
  
# using slicing to left rotate by 3
test_list = test_list[3:] + test_list[:3]
  
# Printing list after left rotate
print ("List after left rotate by 3 : " + str(test_list))
  
# using slicing to right rotate by 3
# back to Original
test_list = test_list[-3:] + test_list[:-3]
  
# Printing after right rotate
print ("List after right rotate by 3(back to original) : "
                                         + str(test_list))

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Output:

Original list : [1, 4, 6, 7, 2]
List after left rotate by 3 : [7, 2, 1, 4, 6]
List after right rotate by 3 ( back to original) : [1, 4, 6, 7, 2]

 
Method #2 : Using list Comprehension
This problem can also be solved by naive method, but its shorter implementation would be with the help of list comprehension. In this method, we just reassign the index to each value to specific position after rotation.

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# Python3 code to demonstrate 
# rotation of list 
# using list comprehension
  
# initializing list
test_list = [1, 4, 6, 7, 2]
  
# printing original list 
print ("Original list : " + str(test_list))
  
# using list comprehension to left rotate by 3
test_list = [test_list[(i + 3) % len(test_list)]
               for i, x in enumerate(test_list)]
  
# Printing list after left rotate
print ("List after left rotate by 3 : " + str(test_list))
  
# using list comprehension to right rotate by 3
# back to Original
test_list = [test_list[(i - 3) % len(test_list)]
               for i, x in enumerate(test_list)]
  
# Printing after right rotate
print ("List after right rotate by 3(back to original) : " 
                                        + str(test_list))

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Output:

Original list : [1, 4, 6, 7, 2]
List after left rotate by 3 : [7, 2, 1, 4, 6]
List after right rotate by 3(back to original) : [1, 4, 6, 7, 2]

 
Method #3 : Using collections.deque.rotate()
The collections module has deque class which provides the rotate(), which is inbuilt function to allow rotation. This is lesser known function but has a greater utility.

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# Python3 code to demonstrate 
# rotation of list 
# using rotate()
from collections import deque
  
# initializing list
test_list = [1, 4, 6, 7, 2]
  
# printing original list 
print ("Original list : " + str(test_list))
  
# using rotate() to left rotate by 3
test_list = deque(test_list)
test_list.rotate(-3)
test_list = list(test_list)
  
# Printing list after left rotate
print ("List after left rotate by 3 : " + str(test_list))
  
# using rotate() to right rotate by 3
# back to Original
test_list = deque(test_list)
test_list.rotate(3)
test_list = list(test_list)
  
# Printing after right rotate
print ("List after right rotate by 3(back to original) : "
                                        + str(test_list))

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Output:

Original list : [1, 4, 6, 7, 2]
List after left rotate by 3 : [7, 2, 1, 4, 6]
List after right rotate by 3(back to original) : [1, 4, 6, 7, 2]


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