获取列中具有特定值的最后一行，Python

Question

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!

Answer 1

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.

Answer 2

当您的数据未排序时，这也将起作用：

df[df.ok == 'x'][df.data == df.data.min()]