Python 如何更新列'；基于另一行的数据帧中的s值？

假设我有以下数据框：

id action  timestamp           time_difference opened
1  sent    2017-06-29 18:38:03 _NaN_           _NaN_
1  clicked 2017-06-29 18:40:03 _NaN_           _NaN_
2  sent    2017-06-29 18:38:03 _NaN_           _NaN_

我希望最终结果是一行，第二行合并到前一行。将计算时差标签，如果找到具有“已单击”状态的匹配id，则打开的标签将设置为1

id action  timestamp           time_difference opened
1  sent    2017-06-29 18:38:03 00:02:00        1
2  sent    2017-06-29 18:38:03 _NaN_           0

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创建两个数据集-一个用于发送，一个用于单击，并在id上合并它们，然后进行计算

import pandas as pd
df['timestamp'] = pd.to_datetime(df['timestamp'])
df_sent = df[df['action']=='sent'][['id', 'timestamp']]
df_clicked = df[df['action']=='clicked'][['id', 'timestamp']]
df_clicked.columns = ['id', 'ts_clicked']

dfm = df_sent.merge(df_clicked, on='id', how='left')
dfm['time_difference'] = dfm['ts_clicked'] - dfm['timestamp']
dfm['opened'] = pd.notnull(dfm['ts_clicked'])*1
dfm = dfm[['id', 'timestamp', 'time_difference', 'opened']]