ValueError: at least one array or dtype is required

This error occurs when you try to perform an operation that requires at least one array or data type, but none is provided or specified incorrectly.

For example, if you are trying to create a NumPy array but do not provide any values, you will get this error:

import numpy as np

arr = np.array()
# ValueError: at least one array or dtype is required

To fix this, you need to provide some values for the array:

arr = np.array([1, 2, 3])

Another example is when you try to concatenate arrays but do not specify which axis to concatenate along:

import numpy as np

arr1 = np.array([[1, 2], [3, 4]])
arr2 = np.array([[5, 6], [7, 8]])

arr = np.concatenate((arr1, arr2))
# ValueError: all the input array dimensions for the concatenation axis must match exactly

To fix this, you need to specify the axis to concatenate along:

arr = np.concatenate((arr1, arr2), axis=0)

Overall, the ValueError: at least one array or dtype is required error is a reminder to make sure you provide the necessary inputs for the operation you are performing.