Python Array Rotation
You can rotate a list in place in Python by using a deque:
>>> from collections import deque>>> d=deque([1,2,3,4,5])>>> ddeque([1, 2, 3, 4, 5])>>> d.rotate(2)>>> ddeque([4, 5, 1, 2, 3])>>> d.rotate(-2)>>> ddeque([1, 2, 3, 4, 5])Or with list slices:
>>> li=[1,2,3,4,5]>>> li[2:]+li[:2][3, 4, 5, 1, 2]>>> li[-2:]+li[:-2][4, 5, 1, 2, 3]Note that the sign convention is opposite with deque.rotate vs slices.
If you want a function that has the same sign convention:
def rotate(l, y=1): if len(l) == 0: return l y = -y % len(l) # flip rotation direction return l[y:] + l[:y]>>> rotate([1,2,3,4,5],2)[4, 5, 1, 2, 3]>>> rotate([1,2,3,4,5],-22)[3, 4, 5, 1, 2]>>> rotate('abcdefg',3)'efgabcd'For numpy, just use np.roll
>>> aarray([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])>>> np.roll(a, 1)array([9, 0, 1, 2, 3, 4, 5, 6, 7, 8])>>> np.roll(a, -1)array([1, 2, 3, 4, 5, 6, 7, 8, 9, 0])Or you can use a numpy version of the same rotate above (again noting the difference in sign vs np.roll):
def rotate(a,n=1): if len(a) == 0: return a n = -n % len(a) # flip rotation direction return np.concatenate((a[n:],a[:n]))
I found a problem that I needed Right and Left rotations for big values of k (where k is number of rotations), so, I implemented the following functions for any size of k.
Right Circular Rotation (left to the right: 1234 -> 4123):
def right_rotation(a, k): # if the size of k > len(a), rotate only necessary with # module of the division rotations = k % len(a) return a[-rotations:] + a[:-rotations]Left Circular Rotation (right to the left: 1234 -> 2341):
def left_rotation(a, k): # if the size of k > len(a), rotate only necessary with # module of the division rotations = k % len(a) return a[rotations:] + a[:rotations]Sources: