First of all I’m not sure if it is the correct title. Feel free to suggest a better one.

This is my DataFrame:

import pandas as pd
df = pd.DataFrame(
    {
        'a': [100, 100, 102, 102, 106, 106, 106, 107, 107, 107]
    }
)

And this is the expected output. I want to create column b:

     a    b
0  100    100  
1  100    100
2  102    103
3  102    103
4  106    106.09
5  106    106.09
6  106    106.09
7  110    110
8  110    110
9  110    110

The process is as follows:

a) Groups are defined by column a.

b) Each group must be AT LEAST 3 percent higher than the previous group. That is the output of column b.

For example:

First group is 100. So the process starts for the next group.

100 * 1.03 = 103

The next group is 102. It is less than 103. So for b, 103 is selected. Now the next group is 106 so:

103 * 1.03 = 106.09

106 is less than this number so 106.09 is selected. For the next group since 110 > 106.09 * 1.03, 110 is selected.

This is one of my attemps. But it feels like it is not the correct approach:

df['streak'] = df.a.ne(df.a.shift(1)).cumsum()
df['b'] = df.groupby('streak')['a'].apply(lambda x: x * 1.03)