pandas 在一个列上按最大日期分组在另一列上

问题描述

我有一个包含以下数据的数据框:

i have a dataframe with following data :

invoice_no  dealer  billing_change_previous_month        date
       110       1                              0  2016-12-31
       100       1                         -41981  2017-01-30
      5505       2                              0  2017-01-30
      5635       2                          58730  2016-12-31

我只希望有一个最大日期的经销商.所需的输出应如下所示:

i want to have only one dealer with the maximum date . The desired output should be like this :

invoice_no  dealer  billing_change_previous_month        date
       100       1                         -41981  2017-01-30
      5505       2                              0  2017-01-30

每个经销商的最大日期应有所不同，预先感谢您的帮助.

each dealer should be distinct with maximum date,thanks in advance for your help.

推荐答案

您可以使用groupby和transform来使用布尔索引

You can use boolean indexing using groupby and transform

df_new = df[df.groupby('dealer').date.transform('max') == df['date']]

    invoice_no  dealer  billing_change_previous_month   date
1   100         1       -41981                          2017-01-30
2   5505        2       0                               2017-01-30

如果有两个以上的经销商，

If there are more than two dealers,

df = pd.DataFrame({'invoice_no':[110,100,5505,5635,10000,10001], 'dealer':[1,1,2,2,3,3],'billing_change_previous_month':[0,-41981,0,58730,9000,100], 'date':['2016-12-31','2017-01-30','2017-01-30','2016-12-31', '2019-12-31', '2020-01-31']})

df['date'] = pd.to_datetime(df['date'])
df[df.groupby('dealer').date.transform('max') == df['date']]


    invoice_no  dealer  billing_change_previous_month   date
1   100         1       -41981                          2017-01-30
2   5505        2       0                               2017-01-30
5   10001       3       100                             2020-01-31

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