NumPy Create an Empty Array or Matrix: A Beginner Guide – NumPy Tutorial

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5 years ago

Empty array and matrix is an important data in numpy. In this tutorial, we will introduce how to create them using some simple examples.

Can numpy.empty() create an empty array?

The answer is not, numpy.empty() function can not create an empty array.

Here is detail.

To create an empty array is very easy in numpy. Here is an example:

import numpy as np

ex = np.array([], dtype = np.float32)
print(ex)
print(ex.shape)

The ex is:

[]
(0,)

We can use ndarray.size to check. Here is an tutorial.

This is an very import tip for numpy programming. We can concatenate an empty array with other non-empty numpy array. Here is an example:

x2 = np.array([1, 2, 3, 4], dtype = np.float32)
x = np.concatenate((ex, x2), axis = 0)
print(x)

Here ex is an empty array, x2 is not empty. We can concatenate them. The result x is:

[1. 2. 3. 4.]

Similar to empty array, we also can create an empty matrix in numpy.

We can create an empty numpy matrix as code below:

import numpy as np

em = np.mat([], dtype = np.float32)
print(em)
print(em.shape)

Here em is an empty numpy matrix. We also can use em.size to check a numpy matrix is empty or not.

em is:

[]
(1, 0)

Notice: you should notice the shape of empty array ex and empty matrix em is not.

ex	(0,)
em	(1,0)