[FIXED] How to get the maximum value of a continuous condition being true?

Issue

How the TRUE_MAX column is calculated?

Input:

import pandas as pd
A=[28,30,15,25,24,13,31,19,20,11,19,21]
COND=[False,True,True,True,False,False,True,True,True,False,True,True]
df=pd.DataFrame({'A':A,'COND':COND})

Expected Output

    A   COND    TRUE_MAX
0   28  FALSE   
1   30  TRUE    30
2   15  TRUE    30
3   25  TRUE    30
4   24  FALSE   
5   13  FALSE   
6   31  TRUE    31
7   19  TRUE    31
8   20  TRUE    31
9   11  FALSE   
10  19  TRUE    21
11  21  TRUE    21  

Solution

You could try as follows:

import pandas as pd
A=[28,30,15,25,24,13,31,19,20,11,19,21]
COND=[False,True,True,True,False,False,True,True,True,False,True,True]
df=pd.DataFrame({'A':A,'COND':COND})

# splitting your data in groups: 1 through to 6
sequences = (df.COND != df.COND.shift()).cumsum()

# use only groups where df.COND == True and for each group get max in df.A
max_vals = df[df.COND].groupby(sequences)['A'].transform(max)

# assign to orig df
df['TRUE_MAX'] = max_vals
print(df)

     A   COND  TRUE_MAX
0   28  False       NaN
1   30   True      30.0
2   15   True      30.0
3   25   True      30.0
4   24  False       NaN
5   13  False       NaN
6   31   True      31.0
7   19   True      31.0
8   20   True      31.0
9   11  False       NaN
10  19   True      21.0
11  21   True      21.0

Answered By - ouroboros1