Invalid entry 0 in condlist: should be boolean ndarray

When you see the error message “invalid entry 0 in condlist: should be boolean ndarray” in Python, it means that there is an issue with the condition list provided to a NumPy function or method.

The error occurs when the condition list provided is not a boolean ndarray (N-dimensional array). The condition list should be a NumPy array consisting of boolean values (True or False) to be used as a mask or filter.

Here is an example to illustrate the error:

import numpy as np

arr = np.array([1, 2, 3, 4, 5])
mask = [True, False, True, False, True]

result = np.extract(mask, arr)  # Raises "invalid entry 0 in condlist: should be boolean ndarray" error

In the above example, the variable “mask” is not a boolean ndarray. Instead, it is a regular Python list. Therefore, when trying to use the “mask” as a condition list in the “np.extract()” function from NumPy, the error is raised.

To fix the error, you need to ensure that the condition list passed to the function is a boolean ndarray. Here’s the corrected example:

import numpy as np

arr = np.array([1, 2, 3, 4, 5])
mask = np.array([True, False, True, False, True])

result = np.extract(mask, arr)  # No error

In the corrected example, the “mask” variable is converted into a boolean ndarray using the “np.array()” function. Now, when “mask” is passed to the “np.extract()” function, the error is resolved, and the extraction operation is performed successfully.