736 fix matched pair flag

[robertswh]

Pull Request Title

Fix matched pair flag

Summary

This request implements ASAP-736 by fixing the matched pair flag function. Also ran into some issues with the ratio_of_means unit tests as a result of this change, so also needed to fix those issues (primarily fixed by adding in the imputation_flag column that the function needed, fixing a bug in join_manual_constructions where a column was duplicated and dropping some columns from expected outputs).

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Checklists

This pull request meets the following requirements:

Creator Checklist

• 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 docstrings
• 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

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

Reviewer Checklist

• Test suite passes (locally as a minimum)
• Peer reviewed with review recorded

Additional Information

Please provide any additional information or context that would help the reviewer understand the changes in this pull request.

Related Issues

Link any related issues or pull requests here.

[AntonZogk]

for future reference fill_group could be used here ( highlighted the wrong rows, i was referring line 60)

[NathanKelly-ONS]

Thanks Anton, would love to hear more about this - I tried searching "fill_group pandas" but nothing is coming up!

[AntonZogk]

All looking good, just one comment which needs sorting