Here’s a dataframe, with some parameters for each id by some regular quarterly dates. It’s originally shuffled randomly, but, at first, let say, it is sorted by fab_date and id.

import pandas as pd
np.random.seed(1)
dt_to_fun = pd.DataFrame({
    'fab_date': pd.to_datetime(["2022-01-01", "2022-07-01", "2023-01-01", "2023-07-01",
                                "2022-01-01", "2022-07-01", "2023-01-01", "2023-07-01",
                                "2022-01-01", "2022-07-01", "2023-01-01", "2023-07-01"]),
    'id': ['n_01', 'n_01', 'n_01', 'n_01', 'n_02', 'n_02', 'n_02', 'n_02', 'n_03', 'n_03', 'n_03', 'n_03'],
    'param_01': np.random.choice([10, 20, 30], size=12),
    'param_02': np.random.choice([10, 30, 50], size=12)
})

dt_to_fun
    fab_date    id  param_01    param_02
0   2022-01-01  n_01    20  30
1   2022-07-01  n_01    10  50
2   2023-01-01  n_01    10  10
3   2023-07-01  n_01    20  50
4   2022-01-01  n_02    20  30
5   2022-07-01  n_02    10  50
6   2023-01-01  n_02    10  10
7   2023-07-01  n_02    20  10
8   2022-01-01  n_03    10  50
9   2022-07-01  n_03    20  10
10  2023-01-01  n_03    10  30
11  2023-07-01  n_03    30  50

The goal is: for each id replace (last date) param value like this: param_01(last date) = param_01(last date) + param_01(-1 date) – param_01(-2 date)
For example, id n_03 last value of param_02 is 50, previous is 30, two times earlier is 10, so the result should be 50 + 30 – 10 = 70. The same for each id and all param* columns. Only parameters in rows with last date for each id should be updated.

Resulting table should be like this:

dt_to_fun
    fab_date    id  param_01    param_02
0   2022-01-01  n_01    20  30
1   2022-07-01  n_01    10  50
2   2023-01-01  n_01    10  10
3   2023-07-01  n_01    20  10
4   2022-01-01  n_02    20  30
5   2022-07-01  n_02    10  50
6   2023-01-01  n_02    10  10
7   2023-07-01  n_02    20  -30
8   2022-01-01  n_03    10  50
9   2022-07-01  n_03    20  10
10  2023-01-01  n_03    10  30
11  2023-07-01  n_03    20  70

I’ve tried applymap, shift etc, but can not figure out, how this all should work together. Would appreciate any help.