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Numpy – Reverse the Sign of Values in Array

Numpy arrays are very versatile when it comes to performing numerical operations on them. Also, the Numpy library comes with a number of useful built-in functions to work with and manipulate the data in arrays. In this tutorial, we will look at how to reverse the sign of values in a Numpy array with the help of some examples.

How to reverse the sign of values in a Numpy Array?

reverse the sing of values in numpy array

To reverse the sign of each value in a Numpy array, you can either multiply the entire array by -1 or use the numpy.negative() function.

The following is the syntax –

## reverse the sign of array elements
# multiply by -1
-1 * ar
# use numpy.negative()
numpy.negative(ar)

Both methods return a Numpy array with the sign of the values reversed.

Examples

Let’s now look at a step-by-step example of using the above methods to reverse the sign of values in a Numpy array.

Step 1 – Create a Numpy array

First, we will create a Numpy array that we will be using throughout the tutorial.

import numpy as np

# create array
ar = np.array([-2, -1, 0, 1, 2, 3, 3.4])
# display the array
print(ar)

Output:

[-2.  -1.   0.   1.   2.   3.   3.4]

Here, we used the numpy.array() function to create a Numpy array with some numeric values. You can see that the array contains both positive and negative values (along with a zero).

Step 2 – Reverse the sign of values in the array

There are two ways you can reverse the sign of each element –

Multiply the array by -1

Multiply the Numpy array with the scaler value -1.

# reverse the sign
-1*ar

Output:

array([ 2. ,  1. , -0. , -1. , -2. , -3. , -3.4])

The resulting array has the sign of each value reversed.

Use the numpy.negative() function

Alternatively, you can also use the numpy.negative() function. This function returns the element-wise numerical negative of the array.

Let’s apply this function to the same array we used above.

# reverse the sign
np.negative(ar)

Output:

array([ 2. ,  1. , -0. , -1. , -2. , -3. , -3.4])

We get the same result as above.

You can also similarly use these methods on higher dimensional arrays to reverse the sign.

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Author

  • Piyush is a data scientist passionate about using data to understand things better and make informed decisions. In the past, he's worked as a Data Scientist for ZS and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.