The error message “cannot subtract datetimearray from ndarray” is encountered when trying to perform a subtraction operation between an array with datetime values (datetimearray) and an array with numerical values (ndarray).
This error occurs because datetime values are not directly compatible with numerical values and subtraction between them is not supported.
To better illustrate this error, let’s consider an example. Assume we have two arrays: one containing datetime values and another containing numerical values.
import numpy as np
dates = np.array(['2022-01-01', '2022-01-02', '2022-01-03'], dtype='datetime64')
numbers = np.array([1, 2, 3])
result = dates - numbers
print(result)
The above code attempts to subtract the numerical values in the “numbers” array from the datetime values in the “dates” array. However, it will result in the “cannot subtract datetimearray from ndarray” error.
To resolve this error, you need to ensure that both arrays are of compatible types or perform the desired operation in a way that is supported by the data types involved. For example, if you want to subtract a fixed time duration from each datetime value, you can use the “numpy.timedelta64” function.
import numpy as np
dates = np.array(['2022-01-01', '2022-01-02', '2022-01-03'], dtype='datetime64')
duration = np.timedelta64(1, 'D')
result = dates - duration
print(result)
In the above code, we create a “duration” variable with a time duration of 1 day. Then we subtract this duration from each datetime value in the “dates” array. This will give us the desired result without encountering the “cannot subtract datetimearray from ndarray” error.
Therefore, it is crucial to ensure that the data types of the arrays involved in subtraction operations are compatible or use appropriate functions to perform the desired calculations.