How to fix ValueError: The truth value of an array with zero elements is ambiguous?

This error arises when you attempt to use an empty array in a conditional context, such as within if-statements or while-loops. This indicates that the truth value of an empty array is ambiguous because it lacks elements to evaluate.

Here is an example code that can produce this error:

import numpy as np

arr = np.array([])
if arr:
    print("The array is not empty")

In this code, the arr variable is an empty NumPy array. When we try to use arr as a condition in the if-statement, the error occurs because there is no value to evaluate.

See also How to use gradient in Numpy

To resolve this error, ensure the array’s length is greater than zero before utilizing it in a conditional statement:

import numpy as np

arr = np.array([])
if len(arr) > 0:
    print("The array is not empty")

In this code, we first check if the length of the array is greater than zero before using it as a condition in the if-statement. This ensures that the code within the if-block executes only when the array contains elements, preventing the error.