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In this chapter, we will discuss about NumPy – roll axis. This function rolls the specified axis backward until it lies in a specified position. The function takes three parameters.

numpy.rollaxis(arr, axis, start)

Where,

Example of NumPy roll axis

# It creates 3 dimensional ndarray 
import numpy as np 
a = np.arange(8).reshape(2,2,2) 

print 'The original array:' 
print a 
print '\n'
# to roll axis-2 to axis-0 (along width to along depth) 

print 'After applying rollaxis function:' 
print np.rollaxis(a,2)  
# to roll axis 0 to 1 (along width to height) 
print '\n' 

print 'After applying rollaxis function:' 
print np.rollaxis(a,2,1)

Its output is as follows −

The original array:
[[[0 1]
 [2 3]]
 [[4 5]
 [6 7]]]

After applying rollaxis function:
[[[0 2]
 [4 6]]
 [[1 3]
 [5 7]]]

After applying rollaxis function:
[[[0 2]
 [1 3]]
 [[4 6]
 [5 7]]]