Join columns to make target columns available at source level

[lars-reimann]

What problem do you want to solve?

Closes #708

Add a join_numpy function to make target columns available at the source level.

The function gets

• Foreign keys,
• Primary keys,
• Targets in the same order as the primary key.

It then maps each foreign key to the associated target. Primary keys must be unique and foreign keys must point to some primary key.

Todo

• [X] Pick an appropriate title.
• [X] Put Closes #XXXX in the first PR comment to auto-close the relevant issue once the PR is accepted. This is not applicable if there is no corresponding issue.
• [x] Document PR in CHANGES.md.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 78.26087% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 89.41%. Comparing base (284bfb3) to head (add6232).

Files	Patch %	Lines
src/_gettsim/shared.py	70.58%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #722 +/- ## ========================================== - Coverage 89.49% 89.41% -0.09% ========================================== Files 51 51 Lines 3627 3646 +19 ========================================== + Hits 3246 3260 +14 - Misses 381 386 +5 ```

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[MImmesberger]

I think the most straightforward application is in function _unterhaltsvors_anspruch_pro_kind_m. There, we need to replace _unterhaltsvorschuss_eink_above_income_threshold_fg. Instead, we should have a bool based on the parent's (linked via p_id_kindergeld_empf) return value of _unterhaltsvorschuss_eink_above_income_threshold.

In Lars' terminology:

• target: _unterhaltsvorschuss_eink_above_income_threshold
• primary key: p_id
• foreign key: p_id_kindergeld_empf

[lars-reimann]

I think the most straightforward application is in function _unterhaltsvors_anspruch_pro_kind_m. There, we need to replace _unterhaltsvorschuss_eink_above_income_threshold_fg. Instead, we should have a bool based on the parent's (linked via p_id_kindergeld_empf) return value of _unterhaltsvorschuss_eink_above_income_threshold.

Thanks, the demo is now included.

[lars-reimann]

I'll look into updating the type hint check later.

[MImmesberger]

Thanks, the demo is now included.

Thanks! I just adjusted the column name and removed the obsolete aggregation dict at the top of the file.

I'm happy with the implementation but I'll let @hmgaudecker approve.