Getting the last non-nan index of a sorted numpy matrix or pandas dataframe

Question

Given a numpy array (or pandas dataframe) like this:

import numpy as np

a = np.array([
[1,      1,      1,    0.5, np.nan, np.nan, np.nan],
[1,      1,              


        

Answer 1

check if not nan then reverse order of columns and take argmax then subtract from number of columns

a.shape[1] - (~np.isnan(a))[:, ::-1].argmax(1) - 1

array([3, 2, 6, 3, 0, 3])