Python 如何在数据帧上选择与重复id匹配的特定字符串的值？

我有这个数据框：

user_id  event 
1        registration
1        visit
1        purchase
2        registration
2        external

我想从至少有一个外部类型事件的每个用户id中选择所有值，以便将它们存储在另一个数据帧中。因此，对于本例，我希望有一个包含下一个信息的数据帧：

user_id  event
2        registration
2        external

---

我该怎么做呢？

您可以计算范围内的用户ID。然后应用布尔掩码：

# calculate unique in-scope IDs
ids = df.loc[df['event'] == 'external', 'user_id'].unique()

# mask dataframe with Boolean series
res = df[df['user_id'].isin(ids)]

print(res)

   user_id         event
3        2  registration
4        2      external

---

您可以计算范围内的用户ID。然后应用布尔掩码：

# calculate unique in-scope IDs
ids = df.loc[df['event'] == 'external', 'user_id'].unique()

# mask dataframe with Boolean series
res = df[df['user_id'].isin(ids)]

print(res)

   user_id         event
3        2  registration
4        2      external

你需要

 #find the user ids wchich has `external`
 user=df[df['event'].isin(['external'])]['user_id']
 #df, which has users
 df[df['user_id'].isin(user)]

你需要

 #find the user ids wchich has `external`
 user=df[df['event'].isin(['external'])]['user_id']
 #df, which has users
 df[df['user_id'].isin(user)]