I have
df = pd.DataFrame('data', car, 'ok')
df:
data car ok
2020-03-25 A
2020-04-01 A x
2020-04-15 A
2020-05-08 A x
2020-06-25 A x
2020-06-27 A
2020-07-15
I want to select last (old in this case) row being column 'ok' with "x"
I want to obtain
2020-04-01 A x
Thanks!
The head() method on DataFrame can give you the first n rows of a DataFrame. Indexing of a DataFrame will allow you to select rows meeting your filter criteria - to narrow to a subset DataFrame with such rows. Together, you could use them to do:
r = df.loc[df.ok == 'x', :].head(1)
What you are doing here is narrowing to a subset DataFrame where ok is 'x' (the df.loc[df.ok == 'x', :] part), then taking the first row of it (the .head(1) part). This of course assumes the DataFrame is sorted by date as it is above.
Indexing is a huge and fundamental topic (think of it as the SQL WHERE of pandas) so you should spend time gaining a deep knowledge of it. Here is a great tutorial. This one and this one are also good.
This will work also when your data is not sorted:
df[df.ok == 'x'][df.data == df.data.min()]