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Python | Ways to rotate a list

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  • Difficulty Level : Basic
  • Last Updated : 12 Sep, 2022
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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 programmer’s life to achieve various tasks. Let’s discuss different ways we can rotate a list in Python

Method 1: Rotate a list using Slicing 

This particular method is the generic method and is mostly employed to achieve this task and has 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. 

Python3




# 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))

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: Rotate a list using list Comprehension 

This problem can also be solved by the 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 the specific position after rotation. 

Python3




# 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))

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: Rotate a list using collections.deque.rotate() 

The collections module has a deque class that provides the rotate(), which is an inbuilt function to allow rotation. This is a lesser-known function but has a greater utility. 

Python3




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))

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 4: Rotate a list using Numpy

In this method, we will use Numpy.roll module to roll the list at a given position, i.e. we are rolling the list at position index 1.

Python3




import numpy as np
 
if __name__ == '__main__':
 
    nums = [11, 4, 6, 7, 8, 33]
    k = 1
 
    x = np.roll(nums, k)
    print(x)

Output:

[33 11  4  6  7  8]

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