[pandas] Find the first element that is -1

[ThomasL]

You can do this very fast with numpy

import numpy as np

a = np.array([[58,  68,  58,   59,   -1, -1], 
              [59,  69,  59,   -1,   -1, -1], 
              [93,  94,  93,   33,   -1, -1], 
              [58,  59,  58,   68,   -1, -1], 
              [92,  94,  92,   33,   -1, -1]])

print(np.sum((a != -1), axis=1))

which outputs a list with the "length" of each row

[4 3 4 4 4]