NumPy Array Flipping

Common array flip methods and other methods

numpy.transpose

The numpy.transpose function is used to swap the dimensions of an array, with the format as follows:

numpy.transpose(arr, axes)

Parameter Description:

arr: The array to be operated onaxes: List of integers, corresponding to dimensions, usually all dimensions will be swapped.

import numpy as np
　
a = np.arange(12).reshape(3,4)
　
print ('Original array:')
print (a )
print ('\n')
　
print ('Swap array:')
print (np.transpose(a))

The output is as follows:

Original array:
[[　0　1　2　3]
　[　4　5　6　7]
　[　8　9　10　11]]
Swap array:
[[　0　4　8]
　[　1　5　9]
　[　2　6　10]
　[　3　7　11]]

The numpy.ndarray.T is similar to numpy.transpose:

import numpy as np
a = np.arange(12).reshape(3,4)
　
print ('Original array:')
print (a)
print ('\n')
　
print ('Transpose array:')
print (a.T)

The output is as follows:

Original array:
[[　0　1　2　3]
　[　4　5　6　7]
　[　8　9　10　11]]
Transpose array:
[[　0　4　8]
　[　1　5　9]
　[　2　6　10]
　[　3　7　11]]

numpy.rollaxis

The numpy.rollaxis function rolls a specific axis to a specific position, with the format as follows:

numpy.rollaxis(arr, axis, start)

Parameter Description:

arr: Arrayaxis: The axis to roll back, the relative positions of other axes will not changestart: Default is zero, indicating a full roll. It will roll to a specific position.

import numpy as np
　# Created a three-dimensional ndarray
a = np.arange(8).reshape(2,2,2)
　
print ('Original array:')
print (a)
print ('\n')
　# Roll axis　2　Roll axis 0 (width to depth)
　
print ('Calling the rollaxis function:')
print (np.rollaxis(a,2))
　# Roll axis 0 to axis　1(Width to height)
print ('\n')
　
print ('Calling the rollaxis function:')
print (np.rollaxis(a,2,1))

The output is as follows:

Original array:
[[[0　1]
　　[2　3]]
　[[4　5]
　　[6　7]]]
Calling the rollaxis function:
[[[0　2]
　　[4　6]]
　[[1　3]
　　[5　7]]]
Calling the rollaxis function:
[[[0　2]
　　[1　3]]
　[[4　6]
　　[5　7]]]

numpy.swapaxes

The numpy.swapaxes function is used to swap two axes of an array, the format is as follows:

numpy.swapaxes(arr, axis1, axis2)

arr: Input arrayaxis1: Integer corresponding to the first axisaxis2: Integer corresponding to the second axis

import numpy as np　
　# Created a three-dimensional ndarray
a = np.arange(8).reshape(2,2,2)
　
print ('Original array:')
print (a)
print ('\n')
　# Now swap axis 0 (depth direction) to axis　2(Width direction)
　
print ('The array after calling the swapaxes function:')
print (np.swapaxes(a,　2, 0))

The output is as follows:

Original array:
[[[0　1]
　　[2　3]]
　[[4　5]
　　[6　7]]]
The array after calling the swapaxes function:
[[[0　4]
　　[2　6]]
　[[1　5]
　　[3　7]]]