Minor documentation issue on pd.DataFrame.last_valid_index()

[gabrielclow]

Documentation says "first" on both first and last methods

Pandas version = 0.21.0

[jreback]

first -> last here: https://github.com/pandas-dev/pandas/blob/master/pandas/core/frame.py#L4317

can you do a PR?

[gabrielclow]

I've never done one but I will happily learn how to tonight

[gabrielclow]

Sorry I took too long. Pull request was sent. 😄