Calculate the mean of a row or column, and use the dot multiplication on matrices.

Mean and dot

In [1]:

import numpy as np

In [4]:

# create 3 x 1 array
lst = [[6], [7], [8]]
array = np.array(lst)
array

Out[4]:

array([[6],
       [7],
       [8]])

In [3]:

# create 1 x 3 array
lst_2 = [[2, 2, 2]]
array_2 = np.array(lst_2)
array_2

Out[3]:

array([[2, 2, 2]])

In [5]:

# np.mean(array_name)
# it simply sums up all elements and divide the sum by the number of elements
# this will output a single number
np.mean(array)

Out[5]:

7.0

In [6]:

# np.mean(array_name)
np.mean(array_2)

Out[6]:

2.0

In [9]:

# dot is different from element-wise multiplication

# 3 x 1 dot 1 x 3 
# this would output a 3 x 3 array
np.dot(array, array_2)

Out[9]:

array([[12, 12, 12],
       [14, 14, 14],
       [16, 16, 16]])

Tags: numpy