python-scipyHow can I use the "where" function in Python Numpy?

The where function in Python Numpy can be used to return elements from an array based on a condition. It can be used in two different ways:

1. np.where(condition, x, y): returns elements from x if the condition is true, and elements from y if the condition is false.

Example

import numpy as np

array_1 = np.array([1, 2, 3, 4, 5])
array_2 = np.array([10, 20, 30, 40, 50])

# Return elements from array_1 if the element is greater than 3, else return elements from array_2
result = np.where(array_1 > 3, array_1, array_2)

print(result)

Output example

[10 20 30 4 5]

2. np.where(condition): returns the indices of elements that satisfy the condition.

Example

import numpy as np

array_1 = np.array([1, 2, 3, 4, 5])

# Return the indices of elements that are greater than 3
result = np.where(array_1 > 3)

print(result)

Output example

(array([3, 4]),)

Helpful links

• Numpy where function
• Numpy where function tutorial

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