• I have a dataset. Columns represents different variables.
• A variable may start with NaN or any double type number.
• If it starts with double number it continues with double type numbers.
• If it starts with NaN, we do not know when it ends.
• Return the row index where last NaN is observed in overall dataset. (Think column-wise)

Input

[ 1 NaN 5 NaN 2

2 NaN 4 4 8

6 NaN 8 2 4

0 0 0 0]

should return 3 because last NaN is observed in third row.

Test suite may be changed!