在 Pandas 中，如何根据仅影响某些条目的条件过滤所有行以获得唯一 ID？

Question

I am working with a dataframe like this:

import pandas as pd
import datetime
records = [{'Name':'John', 'Start':'2020-01-01','Stop':'2020-03-31'}, {'Name':'John', 'Start':'2020-04-01','Stop':'2020-12-31'}, 
       {'Name':'Mary', 'Start':'2020-01-01','Stop':'2020-03-15'}, {'Name':'Mary', 'Start':'2020-03-16','Stop':'2020-03-31'}, 
       {'Name':'Mary', 'Start':'2020-04-01','Stop':'2020-12-31'}, {'Name':'Stan', 'Start':'2020-02-01','Stop':'2020-03-31'},
       {'Name':'Stan', 'Start':'2020-04-01','Stop':'2020-12-31'}]
df = pd.DataFrame(records)
df['Start'] = pd.to_datetime(df['Start'])
df['Stop'] = pd.to_datetime(df['Stop'])
df

which gives the output

Name         Start       Stop
0   John    2020-01-01  2020-03-31
1   John    2020-04-01  2020-12-31
2   Mary    2020-01-01  2020-03-15
3   Mary    2020-03-16  2020-03-31
4   Mary    2020-04-01  2020-12-31
5   Stan    2020-02-01  2020-03-31
6   Stan    2020-04-01  2020-12-31

What I want to do is select all the records for all the individuals who have a start date of 2020-01-01. That is, if someone doesn't have a record beginning on 1/1, then I don't want any of their records. The results should give me this:

    Name    Start   Stop
0   John    2020-01-01  2020-03-31
1   John    2020-04-01  2020-12-31
2   Mary    2020-01-01  2020-03-15
3   Mary    2020-03-16  2020-03-31
4   Mary    2020-04-01  2020-12-31

There should be no records for Stan in the output, because none of his entries start with 2020-01-01. Any ideas on how to accomplish this? Thanks!

Answer 1

Try the condition grouped by transform:

df[df['Start'].eq("2020-01-01").groupby(df["Name"]).transform('any')]

---

   Name      Start       Stop
0  John 2020-01-01 2020-03-31
1  John 2020-04-01 2020-12-31
2  Mary 2020-01-01 2020-03-15
3  Mary 2020-03-16 2020-03-31
4  Mary 2020-04-01 2020-12-31