Rotate a Python list

This post will discuss how to rotate a list in Python.

1. Using deque `rotate()` function

The collections.deque is a generalization of stacks and queues and support the rotate() function, which rotates the deque k steps to the right.

from collections import deque

if __name__ == '__main__':

nums = list(range(5))

k = 2

x = deque(nums)

x.rotate(k)

print(x) # [3, 4, 0, 1, 2]

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To rotate k steps to the left, pass the negative value of k, as shown below:

from collections import deque

if __name__ == '__main__':

nums = list(range(5))

k = 2

x = deque(nums)

x.rotate(-k)

print(x) # [2, 3, 4, 0, 1]

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Note that the rotate() takes O(k) time in both the average and amortized worst cases.

2. Using `numpy.roll()` function

If you happen to be using NumPy already, you can use the roll() function that rotates the array elements along a given axis. To right-rotate the sequence by k positions, you can pass the list and an integer denoting the shift to the roll() function, as shown below:

import numpy as np

if __name__ == '__main__':

nums = list(range(5))

k = 2

x = np.roll(nums, k)

print(x) # [3, 4, 0, 1, 2]

The second argument to the roll() function denotes the total number of places by which elements are shifted. To rotate left, pass the negative value of k:

import numpy as np

if __name__ == '__main__':

nums = list(range(5))

k = 2

x = np.roll(nums, -k)

print(x) # [2, 3, 4, 0, 1]

3. Using Slicing

You can also use slicing to create two new lists and return the concatenation of both lists. The following example shows how to rotate the list k positions to the right using slicing:

def rotate(seq, k):

return seq[k:] + seq[:k]

if __name__ == '__main__':

nums = list(range(5))

k = 2

x = rotate(nums, k)

print(x) # [2, 3, 4, 0, 1]

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To left-rotate, pass the negative value of k as before:

def rotate(seq, k):

return seq[k:] + seq[:k]

if __name__ == '__main__':

nums = list(range(5))

k = 2

x = rotate(nums, -k)

print(x) # [3, 4, 0, 1, 2]

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Note that all the above solutions create a new list and does not in-place modify the original list.

That’s all about rotating a list in Python.

1. Using deque rotate() function

2. Using numpy.roll() function

3. Using Slicing

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1. Using deque `rotate()` function

2. Using `numpy.roll()` function