NumPy mean() - Mean of Array
NumPy Mean Function
To calculate mean of elements in a NumPy array, as a whole, or along an axis, or multiple axis, use numpy.mean() function.
In this tutorial we will go through following examples using numpy mean() function.
- Mean of all the elements in a NumPy Array.
- Mean of elements of NumPy Array along an axis.
- Mean of elements of NumPy Array along multiple axis.
Examples
1. Mean of a numpy array
In this example, we take a 2D NumPy Array and compute the mean of the Array.
Python Program
import numpy as np
#initialize array
A = np.array([[2, 1], [5, 4]])
#compute mean
output = np.mean(A)
print(output)
Output
3.0
Mean
Mean = (2 + 1 + 5 + 4)/4
= 12/4
= 3.0
2. Mean of numpy array along an axis
In this example, we take a 2D NumPy Array and compute the mean of the elements along a single, say axis=0.
Pass the named argument axis to mean() function as shown below.
Python Program
import numpy as np
#initialize array
A = np.array([[2, 1], [5, 4]])
#compute mean
output = np.mean(A, axis=0)
print(output)
Output
[3.5 2.5]
Understanding Axis
As we have provided axis=0 as argument, this axis gets reduced to compute mean along this axis, keeping other axis.
[ [2, 1], [5, 4] ]
axis: 0 1 1
[2, 1] and [5, 4] are the elements of axis=0.
Mean
Mean = ([2, 1] + [5, 4])/2
= [(2 + 5)/2, (1 + 4)/2]
= [7/2, 5/2]
= [3.5, 2.5]
3. Mean of numpy array along multiple axis
In this example, we take a 3D NumPy Array, so that we can give atleast two axis, and compute the mean of the Array.
Pass the named argument axis, with tuple of axes, to mean() function as shown below.
Python Program
import numpy as np
#initialize array
A = np.array([[[2, 1], [5, 4]], [[3, 9], [6, 8]]])
#compute mean
output = np.mean(A, axis=(0, 1))
print(output)
Output
[4. 5.5]
Understanding Axis
As we have provided axis=(01 1) as argument, these axis gets reduced to compute mean along this axis, keeping other axis. which is axis: 2.
[ [ [2, 1], [5, 4]], [ [3, 9], [6, 8] ] ]
axis: 0 1 2 2 1 2 2
[[2, 1], [5, 4]] and [[3, 9], [6, 8]] are the elements of axis=0.
[2, 1], [5, 4], [3, 9], [6, 8] are the elements of axis=1.
Mean
Mean = ([2, 1] + [5, 4] + [3, 9] + [6, 8])/4
= [(2 + 5 + 3 + 6)/4, (1 + 4 + 9 + 8)/4]
= [4.0, 5.5]
Summary
In this NumPy Tutorial, we learned how to find mean of a Numpy, of a whole array, along an axis, or along multiple axis, with the help of well detailed Python example programs.