Use stacked ambiguous date checking

[victorlin]

Description of proposed changes

Previously, the ambiguous date checks were 1:1 with the generated date columns. This should not be the case since month needs to check for ambiguous year, and week needs to check for anything that is ambiguous.

Separate the ambiguous date checking from the column generation, and update the conditions for the former to be "stacking" (i.e. year is always checked, month is checked for month/week, and day is checked for week only).

Related issue(s)

Fixes #1071

Testing

• Existing test updated
• Checks pass

Checklist

• Add a message in CHANGES.md summarizing the changes in this PR. Keep headers and formatting consistent with the rest of the file.

[codecov]

Codecov Report

Attention: Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.

Project coverage is 61.83%. Comparing base (0826806) to head (0a8760c).
Report is 1171 commits behind head on master.

Files	Patch %	Lines
augur/filter.py	90.90%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1072      +/-   ##
==========================================
+ Coverage   61.80%   61.83%   +0.02%     
==========================================
  Files          52       52              
  Lines        6321     6331      +10     
  Branches     1551     1558       +7     
==========================================
+ Hits         3907     3915       +8     
  Misses       2141     2141              
- Partials      273      275       +2     

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[joverlee521]

Thank you for tackling this! The changes make sense to me, but I'm just going to play devil's advocate here: Is there any legitimate reason to group by month regardless of year value?

[victorlin]

Is there any legitimate reason to group by month regardless of year value?

There could be, but that would be a separate discussion / feature request since month is already converted to (year, month):

augur/augur/filter.py

Lines 1065 to 1066 in 0a5bfc1

	# month = (year, month)
	metadata['month'] = list(zip(metadata['year'], metadata['month']))

[tsibley]

There could be, but that would be a separate discussion / feature request since month is already converted to (year, month):

Ah, the difference between "month" (a specific one out of an ~infinite set) and "month of the year" (one of the 12).