402 incorrect flags

[AntonZogk]

Summary

The aim is fixing a bug when a target value was not supplied

Checklists

This pull request meets the following requirements:

• installable with all dependencies recorded
• runs without error
• follows PEP8 and project specific conventions
• appropriate use of comments, for example no descriptive comments
• functions documented using Numpy style docstings
• assumptions and decisions log considered and updated if appropriate
• unit tests have been updated to cover essential functionality for a reasonable range of inputs and conditions
• other forms of testing such as end-to-end and user-interface testing have been considered and updated as required
• tests suite passes (locally as a minimum)
• peer reviewed with review recorded

If you feel some of these conditions do not apply for this pull request, please
add a comment to explain why.

Closes #28

[Jday7879]

Great work catching and fixing this issue Anton.
Left some minor reviews with possible suggestions.

[Jday7879]

Hard coding the month offset? variable frequency of data, if supplied every 4 months this would need to be updated.

[Jday7879]

ToDo: cumsum() does not work when date offset is -1.
Might be nice to have but maybe not essential.
Cumsum works top to bottom of a column? Might need to see if that can be reversed.

[AntonZogk]

What this code is trying to do is assign a unique id for the values which meets these criteria (values were sorted):

1. Date difference between 2 rows is the same if you offset them
2. no difference in strata
3. no difference in refence

So hard coded 1 in pd.DateOffset refers to the data frequency and this approach should fail if not monthly data are supplied. The hard coded 1 in the shift and diff refers to the previous row though ( this is why we sorted the data) consequently no reason changing these hard coded values. But if we do we need to change the cumsum to do a reverse order for -1, bellow is the result without cumsum() for values 1 and -1. So for -1 we need to apply cumsum() in reverse order (we can use [::-1].cumsum()), but both 1 and -1 will give the same result ( values will have same integer if same strata, reference and date diffenence is ok) . There is a TODO for now and we can revisit this in the future.

	reference	strata	period	target_variable	fill_group_1	fill_group_-1
0	1	100	2020-01-01 00:00:00	8444	True	False
1	1	100	2020-02-01 00:00:00	nan	False	False
2	1	100	2020-03-01 00:00:00	2003	False	False
3	1	100	2020-04-01 00:00:00	1003	False	True
4	2	100	2020-01-01 00:00:00	nan	True	False
5	2	100	2020-02-01 00:00:00	nan	False	False
6	2	100	2020-03-01 00:00:00	nan	False	False
7	2	100	2020-04-01 00:00:00	3251	False	True
8	3	100	2020-01-01 00:00:00	nan	True	False
9	3	100	2020-02-01 00:00:00	7511	False	False
10	3	100	2020-03-01 00:00:00	1234	False	False
11	3	100	2020-04-01 00:00:00	1214	False	True
12	4	100	2020-01-01 00:00:00	64	True	False
13	4	100	2020-02-01 00:00:00	nan	False	False
14	4	100	2020-03-01 00:00:00	nan	False	False
15	4	100	2020-04-01 00:00:00	254	False	True
16	5	100	2020-01-01 00:00:00	65	True	False
17	5	100	2020-02-01 00:00:00	342	False	False
18	5	100	2020-03-01 00:00:00	634	False	False
19	5	100	2020-04-01 00:00:00	254	False	True
20	6	100	2020-01-01 00:00:00	64	True	False
21	6	100	2020-02-01 00:00:00	nan	False	False
22	6	100	2020-03-01 00:00:00	654	False	False
23	6	100	2020-04-01 00:00:00	nan	False	True
24	7	100	2020-01-01 00:00:00	nan	True	False
25	7	100	2020-02-01 00:00:00	nan	False	False
26	7	100	2020-03-01 00:00:00	nan	False	True