FIX: Handle a non-linear FrameIterator in HydrogenBondAnalysis

[BradyAJohnston]

Fixes #5200

Changes made in this Pull Request:

• If the self.start is None then return computed values by using a dictionary lookup rather than index lookup

LLM / AI generated code disclosure

LLMs or other AI-powered tools (beyond simple IDE use cases) were used in this contribution: no

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• Issue raised/referenced?
• Tests updated/added?
• Documentation updated/added?
• package/CHANGELOG file updated?
• Is your name in package/AUTHORS? (If it is not, add it!)
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I certify that I can submit this code contribution as described in the Developer Certificate of Origin, under the MDAnalysis LICENSE.

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📚 Documentation preview 📚: https://mdanalysis--5202.org.readthedocs.build/en/5202/

[BradyAJohnston]

Oops it seems like my auto-formatter went a bit wild - despite still passing Black. Will clean up.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.73%. Comparing base (a029dcd) to head (ae5afa7).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #5202   +/-   ##
========================================
  Coverage    92.72%   92.73%           
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  Files          180      180           
  Lines        22473    22476    +3     
  Branches      3189     3190    +1     
========================================
+ Hits         20838    20843    +5     
+ Misses        1177     1176    -1     
+ Partials       458      457    -1     

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[orbeckst]

Looks good!

Optionally: Look at the performance, perhaps there's a faster way to do the lookup.

[orbeckst]

Looking up each frame looks slow. Perhaps there's some numpy magic (take???) ?

[BradyAJohnston]

The only really faster approach I could figure out would be this:

  if self.start is None:
      counts = np.zeros(len(self.frames), dtype=int)
      positions = np.searchsorted(self.frames, indices)
      counts[positions] = tmp_counts
      return counts

But this assumes the self.frames to be sorted. Would this always be the case, given the FrameIterator could be a non-sorted sequence of frames?

[orbeckst]

I am not sure if self.frames is sorted, possibly not when using run(frames=[2, 3, 0, 7, 6]). Maybe do a quick test?

Perhaps one could sort frames and rearrange counts in the same way and then un-sort everything again before returning?