How to get the size (e.g. number of elements) of a matrix with numpy in python ?

Examples of how to get the number of elements in an array (or matrix) with numpy in python

Create a matrix

Let's create a simple matrix to illustrate how to get the number of elements

import numpy as np

A = np.random.randint(5, size=(4, 6))

print(A)

returns

[[3 0 0 4 3 3]
 [4 2 3 4 2 2]
 [0 1 1 4 1 0]
 [4 3 0 0 3 3]]

Get the number of elements using size

To get the number of elements in the matrix A, a solution is to use the method size:

print(A.size)

24

Get the number of elements using shape

print(A.shape[0]*A.shape[1])

24

Get the number of unique elements

To go further we can also get unique elements inside the matrix A:

print(np.unique(A))

returns

[0 1 2 3 4]

and then print the number for each unique element:

for e in np.unique(A):
    print('Number of {}: '.format(e), A[A==e].size)

returns

Number of 0:  6
Number of 1:  3
Number of 2:  3
Number of 3:  7
Number of 4:  5

Links

• numpy.ndarray.size