Python delete rows for each group after first occurance in a column

I Have a dataframe as follows:

df = pd.DataFrame({'Key':[1,1,1,1,2,2,2,4,4,4,5,5],
                   'Activity':['A','A','H','B','B','H','H','A','C','H','H','B'],
                   'Date':['2022-12-03','2022-12-04','2022-12-06','2022-12-08','2022-12-03','2022-12-06','2022-12-10','2022-12-03','2022-12-04','2022-12-07','2022-12-03','2022-12-13']})

I need to count the activities for each 'Key' that occur before 'Activity' == 'H' as follows:

Required Output

My Approach

1. Sort df by Key & Date ( Sample input is already sorted)

2. drop the rows that occur after 'H' Activity in each group as follows:

   

3. Groupby df.groupby(['Key', 'Activity']).count()

Is there a better approach , if not then help me in code for dropping the rows that occur after 'H' Activity in each group.

Thanks in advance !

You can bring the H dates "back" into each previous row to use in a comparison.

First mark each H date in a new column:

df.loc[df["Activity"] == "H" , "End"] = df["Date"]

    Key Activity        Date         End
0     1        A  2022-12-03         NaT
1     1        A  2022-12-04         NaT
2     1        H  2022-12-06  2022-12-06
3     1        B  2022-12-08         NaT
4     2        B  2022-12-03         NaT
5     2        H  2022-12-06  2022-12-06
6     2        H  2022-12-10  2022-12-10
7     4        A  2022-12-03         NaT
8     4        C  2022-12-04         NaT
9     4        H  2022-12-07  2022-12-07
10    5        H  2022-12-03  2022-12-03
11    5        B  2022-12-13         NaT

Backward fill the new column for each group:

df["End"] = df.groupby("Key")["End"].bfill()

    Key Activity        Date         End
0     1        A  2022-12-03  2022-12-06
1     1        A  2022-12-04  2022-12-06
2     1        H  2022-12-06  2022-12-06
3     1        B  2022-12-08         NaT
4     2        B  2022-12-03  2022-12-06
5     2        H  2022-12-06  2022-12-06
6     2        H  2022-12-10  2022-12-10
7     4        A  2022-12-03  2022-12-07
8     4        C  2022-12-04  2022-12-07
9     4        H  2022-12-07  2022-12-07
10    5        H  2022-12-03  2022-12-03
11    5        B  2022-12-13         NaT

You can then select rows with Date before End

df.loc[df["Date"] < df["End"]]

   Key Activity        Date         End
0    1        A  2022-12-03  2022-12-06
1    1        A  2022-12-04  2022-12-06
4    2        B  2022-12-03  2022-12-06
7    4        A  2022-12-03  2022-12-07
8    4        C  2022-12-04  2022-12-07

To generate the final form - you can use .pivot_table()

(df.loc[df["Date"] < df["End"]]
   .pivot_table(index="Key", columns="Activity", values="Date", aggfunc="count")
   .reindex(df["Key"].unique()) # Add in keys with no match e.g. `5`
   .fillna(0)
   .astype(int))

Activity  A  B  C
Key              
1         2  0  0
2         0  1  0
4         1  0  1
5         0  0  0

Try this:

(df.loc[df['Activity'].eq('H').groupby(df['Key']).cumsum().eq(0)]
.set_index('Key')['Activity']
.str.get_dummies()
.groupby(level=0).sum()
.reindex(df['Key'].unique(),fill_value=0)
.reset_index())

or

(df['Activity'].where(df['Activity'].ne('H').groupby(df['Key']).cumprod())
.str.get_dummies()
.groupby(df['Key']).sum())

Output:

   Key  A  B  C
0    1  2  0  0
1    2  0  1  0
2    4  1  0  1
3    5  0  0  0

You can try:

# sort by Key and Date
df.sort_values(['Key', 'Date'], inplace=True)

# this is to keep Key in the result when no values are kept after the filter
df.Key = df.Key.astype('category')

# filter all rows after the 1st H for each Key and then pivot
df[~df.Activity.eq('H').groupby(df.Key).cummax()].pivot_table(
  index='Key', columns='Activity', aggfunc='size'
).reset_index()

#Activity Key  A  B  C
#0          1  2  0  0
#1          2  0  1  0
#2          4  1  0  1
#3          5  0  0  0