Groupby +有条件的从另一列创建新的 [英] Groupby + conditional from another column to create new one
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问题描述
我正在尝试在新列( 2nd_visit_date)中捕获用户的 visit_num == 2的日期
I am trying to capture the date of the "visit_num==2" of "users" in a new column ("2nd_visit_date")
下面是代码(包括我要创建的新列)
Here's the code (including the new column I want to create)
df=pd.DataFrame({'user':[1,1,2,2,2,3,3,3,3,3,4,4],
'date':['1995-09-01','1995-09-02','1995-10-03','1995-10-04','1995-10-05','1995-11-07','1995-11-08','1995-11-09','1995-11-10','1995-11-15','1995-12-18','1995-12-20'],
'visit_num':[1,2,1,2,3,1,2,3,4,5,1,2],
'2nd_visit_date':['1995-09-02','1995-09-02','1995-10-04','1995-10-04','1995-10-04','1995-11-08','1995-11-08','1995-11-08','1995-11-08','1995-11-08','1995-12-20','1995-12-20']})
所以我得到:
user date visit_num 2nd_visit_date
1 1995-09-01 1 1995-09-02
1 1995-09-02 2 1995-09-02
2 1995-10-03 1 1995-10-04
2 1995-10-04 2 1995-10-04
2 1995-10-05 3 1995-10-04
3 1995-11-07 1 1995-11-08
3 1995-11-08 2 1995-11-08
3 1995-11-09 3 1995-11-08
3 1995-11-10 4 1995-11-08
3 1995-11-15 5 1995-11-08
4 1995-12-18 1 1995-12-20
4 1995-12-20 2 1995-12-20
我尝试了以下代码,但没有用:
I tried the following code, but it did not work:
df["2nd_visit_date"] = df.groupby("user")["date"].transform(df['visit_num']==2)
任何帮助将不胜感激。谢谢。
Any help will be very much appreciated. Thanks.
推荐答案
让我们说这是您原始的 df
:
Let say this is your original df
:
df
user date visit_num
0 1 1995-09-01 1
1 1 1995-09-02 2
2 2 1995-10-03 1
3 2 1995-10-04 2
4 2 1995-10-05 3
5 3 1995-11-07 1
6 3 1995-11-08 2
7 3 1995-11-09 3
8 3 1995-11-10 4
9 3 1995-11-15 5
10 4 1995-12-18 1
11 4 1995-12-20 2
您可以先为第二次访问创建一个数据框(并更改列名):
You can first create a dataframe for second visits (and change column name):
df_2 = df[df.visit_num==2][['user', 'date']]
df_2.columns = ['user', '2nd_visit_date']
df_2
user 2nd_visit_date
1 1 1995-09-02
3 2 1995-10-04
6 3 1995-11-08
11 4 1995-12-20
并将其与原始 df
合并p>
And merge it with your original df
pd.merge(df, df_2, on='user', how='left')
user date visit_num 2nd_visit_date
0 1 1995-09-01 1 1995-09-02
1 1 1995-09-02 2 1995-09-02
2 2 1995-10-03 1 1995-10-04
3 2 1995-10-04 2 1995-10-04
4 2 1995-10-05 3 1995-10-04
5 3 1995-11-07 1 1995-11-08
6 3 1995-11-08 2 1995-11-08
7 3 1995-11-09 3 1995-11-08
8 3 1995-11-10 4 1995-11-08
9 3 1995-11-15 5 1995-11-08
10 4 1995-12-18 1 1995-12-20
11 4 1995-12-20 2 1995-12-20
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