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')Copy

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)Copy

Output:

[1 2 3 4]Copy

How it works.

First, create a 2-D array:

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

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

b = np.ravel(a)Copy

Third, display the array:

print(b)Copy

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)Copy

How it works.

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

b = np.ravel(a)Copy

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

b[0] = 0Copy

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)Copy

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.

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