how to make col2 the cumsum of the second col1 == 'x' in DateTime per group?-CodePudding

I would like a column in a pandas dataframe that

counts the number of times 'outcome2' is observed in 'value' through 'datetime'
starting from the second observation of 'outcome2'
per 'ID' or df.index

import pandas as pd
from io import StringIO
import datetime 

txt= """
ID,datetime,value
A,12/10/2022 10:00:00,outcome1
A,12/10/2022 11:15:10,outcome2
A,14/10/2022 15:30:30,outcome1
B,11/10/2022 11:30:22,outcome1
B,15/10/2022 22:44:11,outcome2
B,15/10/2022 23:30:22,outcome3
B,15/10/2022 23:31:11,outcome2
"""

df = pd.read_csv(StringIO(txt),\
             parse_dates=[1],\
             dayfirst=True)\
             .assign(id_index= lambda x_df: x_df\
             .groupby('ID', sort=False).ngroup())\
             .set_index("id_index")\
             .rename_axis(index=None)

df = df.assign(value_test = lambda df: df['value']=='outcome2',\
               value_cumsum= lambda df: df.groupby('ID', sort=False)['value_test'].cumsum())

  ID            datetime     value value_test   value_cumsum
0  A 2022-10-12 10:00:00  outcome1      False              0
0  A 2022-10-12 11:15:10  outcome2       True              1
0  A 2022-10-14 15:30:30  outcome1      False              1
1  B 2022-10-11 11:30:22  outcome1      False              0
1  B 2022-10-15 22:44:11  outcome2       True              1
1  B 2022-10-15 23:30:22  outcome3      False              1
1  B 2022-10-15 23:31:11  outcome2       True              2

I tried assigning a third variable to df using if-statements in the lambda functions. It failed in a way others have experienced 1:

df = df.assign(value_test = lambda df: df['value']=='outcome2',\
               value_cumsum = lambda df: df.groupby('ID', sort=False)['value_test'].cumsum(),\
               outcome2 = lambda df: 0 if df[df[value_cumsum]==1] or df[df[value_cumsum]==0]\
               else df[value_cumsum]-1 if df[df[value_cumsum] > 1]

ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

I need only the accumulated sum (running total) of counts of 'outcome2' in 'value' starting from the second observation of 'outcome2' per group.*

Any suggestions, please?

And is it possible to use lambda or without the intermediate step making value_test or value_cumsum?

desired df

  ID            datetime     value outcome2
0  A 2022-10-12 10:00:00  outcome1        0
0  A 2022-10-12 11:15:10  outcome2        0
0  A 2022-10-14 15:30:30  outcome1        0
1  B 2022-10-11 11:30:22  outcome1        0
1  B 2022-10-15 22:44:11  outcome2        0
1  B 2022-10-15 23:30:22  outcome3        0
1  B 2022-10-15 23:31:11  outcome2        1

CodePudding user response：

You can use:

df['value_cumsum'] = (df.groupby('ID')['value_test']
                      .cumsum().sub(1).where(df['value_test'], 0)
                      )

Or, if you also want to label the False:

df['value_cumsum'] = (df.groupby('ID')['value_test']
                      .cumsum().sub(1).clip(lower=0)
                      )

output:

  ID            datetime     value  value_test  value_cumsum
0  A 2022-10-12 10:00:00  outcome1       False             0
0  A 2022-10-12 11:15:10  outcome2        True             0
0  A 2022-10-14 15:30:30  outcome1       False             0
1  B 2022-10-11 11:30:22  outcome1       False             0
1  B 2022-10-15 22:44:11  outcome2        True             0
1  B 2022-10-15 23:30:22  outcome3       False             0
1  B 2022-10-15 23:31:11  outcome2        True             1

without intermediate:

df['value_cumsum'] = (df['value'].eq('outcome2')
                      .groupby(df['ID'])
                      .cumsum().sub(1).clip(lower=0)
                     )

output:

  ID            datetime     value  value_cumsum
0  A 2022-10-12 10:00:00  outcome1             0
0  A 2022-10-12 11:15:10  outcome2             0
0  A 2022-10-14 15:30:30  outcome1             0
1  B 2022-10-11 11:30:22  outcome1             0
1  B 2022-10-15 22:44:11  outcome2             0
1  B 2022-10-15 23:30:22  outcome3             0
1  B 2022-10-15 23:31:11  outcome2             1