Change the size of a numpy array in Python

In this article, we will learn how to change the size of a numpy array in Python.

First, let’s understand what a numpy array is.
A numpy array is a part of the Numpy library which is an array processing package.

import numpy as np
eg_arr = np.array([[1,2],[3,4]])
print(eg_arr)

Using np.array, we store an array of shape (2,2) and size 4 in the variable eg_arr.
numpy array example

Now, let’s see how can we change the size of the array.

Changing size of numpy Array in Python

Size of a numpy array can be changed by using resize() function of Numpy library.

numpy.ndarray.resize() takes these parameters-

  1. New size of the array
  2. refcheck- It is a boolean which checks the reference count. It checks if the array buffer is referenced to any other object. By default it is set to True. You can also set it to False if you haven’t referenced the array to any other object.

During resizing, if the size of the new array is greater than the given size, then the array is filled with 0’s. Also, it resizes the array in-place.

Now let’s understand it with some examples.

Changing size of array with numpy.resize()

Example 1 –

import numpy as np
cd = np.array([2,4,6,8])
cd.resize((3,4),refcheck=False)
print(cd)

The resize function changes the shape of the array from (4,) to (3,4). Since the size of the new array is greater, the array is filled with 0’s.
So this gives us the following output-

Change the size of a numpy array in Python

Example 2 –

import numpy as np 
cd2 = np.array([[1,2],[3,4]]) 
cd2.resize((5,6),refcheck=False)
print(cd2)

The resize function changes the array from (2,2) to (5,6) and fills the remaining portion of the array with 0’s.
Here’s the output-
Change the size of a numpy array in Python

 

import numpy as np
cd3=np.array([[1,2],[3,4]])
cd3.resize((2,1),refcheck=False)
print(cd3)

Here, the size of the new array is smaller, so this gives the following output-
numpy.resize() in Python

I hope you all liked the article!

Also read-
Understanding NumPy array dimensions in Python

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