NumPy ravel()

Summary: in this tutorial, you’ll learn how to use the NumPy ravel() to return a contiguous flattened array.

Introduction to the NumPy ravel() function

The ravel() function accepts an array and returns a 1-D array containing the elements of the input array:

numpy.ravel(a, order='C')Code language: Python (python)

In this syntax:

• a is a numpy array. It can be any array-like object e.g., a list. An array-like object is an object that can be converted into a numpy array.
• order specifies the order of elements. Check out the flatten() method for detailed information on the order parameter and its values.

NumPy ravel() function example

Let’s take some examples of using the ravel() function.

1) Using NumPy ravel() function to flatten an array

The following example uses the ravel() function to flatten a 2-D array:

import numpy as np

a = np.array([[1, 2], [3, 4]])
b = np.ravel(a)

print(b)Code language: Python (python)

Output:

[1 2 3 4]Code language: Python (python)

How it works.

First, create a 2-D array:

a = np.array([[1, 2], [3, 4]])Code language: Python (python)

Second, flatten the array using the ravel() function:

b = np.ravel(a)Code language: Python (python)

Third, display the array:

print(b)Code language: Python (python)

2) ravel() function vs. flatten() method

The flatten() method creates a copy of an input array while the ravel() function creates a view of the array. The ravel() only makes a copy of an array if needed. For example:

import numpy as np

a = np.array([[1, 2], [3, 4]])
b = np.ravel(a)

# change element at index 0
b[0] = 0

# show both b & a array
print(b)
print(a)Code language: Python (python)

How it works.

First, use the ravel() function to create a view of the array a:

b = np.ravel(a)Code language: Python (python)

Second, change the element from index 0 of the array b to zero:

b[0] = 0Code language: Python (python)

Third, show both arrays a and b. Since array b is a view of array a, the change in array b is reflected in array a:

print(b)
print(a)Code language: Python (python)

Another important difference between the flatten() method and ravel() function is that you can call the flatten() method on a ndarray while you can call the ravel() function on an array-like object.

Summary

• Use the numpy ravel() function to return a contiguous flattened array.