NumPy - append() function

The NumPy append() function is used to append values to the end of an array. The syntax for using this function is given below:

Syntax

numpy.append(arr, values, axis=None)

Parameters

Return Value

Returns a copy of array with values appended to axis.

Example: append values on axis=0

In the example below, values array is added on axis=0. Please note that the values array must have same shape as arr, excluding specified axis.

import numpy as np
arr = np.ones((3,3))
values = np.array([[10, 20, 30],[40, 50, 60]])
print("Initial Array:")
print(arr)

print("\nReturned array after append:")
print(np.append(arr, values, axis=0))

The output of the above code will be:

Initial Array:
[[ 1.  1.  1.]
 [ 1.  1.  1.]
 [ 1.  1.  1.]]

Returned array after append:
[[  1.   1.   1.]
 [  1.   1.   1.]
 [  1.   1.   1.]
 [ 10.  20.  30.]
 [ 40.  50.  60.]]

Example: append values on axis=1

When the values array is added on axis=1, please note that the shape of values array.

import numpy as np
arr = np.ones((3,3))
values = np.array([[10, 40], [20, 50], [30, 60]])
print("Initial Array:")
print(arr)

print("\nReturned array after append:")
print(np.append(arr, values, axis=1))

The output of the above code will be:

Initial Array:
[[ 1.  1.  1.]
 [ 1.  1.  1.]
 [ 1.  1.  1.]]

Returned array after append:
[[  1.   1.   1.  10.  40.]
 [  1.   1.   1.  20.  50.]
 [  1.   1.   1.  30.  60.]]

Example: append values on axis=None

When axis is not specified or equal to None, arr and values array are flattened before appending. Consider the following example.

import numpy as np
arr = np.ones((2,2))
values = np.array([10, 20, 30])

print("Returned array after append:")
print(np.append(arr, values, axis=None))

The output of the above code will be:

Returned array after append:
[  1.   1.   1.   1.  10.  20.  30.]