Improve docstring for approximation_grain in ParallelogramOLF

[kennethshsu]

Note

Low Risk
Docstring-only change; no functional or behavioral impact.

Overview
Improves the ParallelogramOLF docstring by documenting the approximation_grain parameter, including supported values ('M' monthly, 'D' daily) and the effect of daily granularity (leap-year handling when assigning factors to origin periods).

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.08%. Comparing base (05ea946) to head (b984f80).

Additional details and impacted files

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  Files          85       85           
  Lines        4896     4896           
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  Hits         4166     4166           
  Misses        521      521           
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Flag	Coverage Δ
unittests	85.08% <ø> (ø)

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[andyhufford-HARC]

First PR Approval. @kennethshsu

[kennethshsu]

Can you actually approve it?🙂

[andyhufford-HARC]

I thought I did approve it. It does say that I have "read-only" permissions and that it requires "at least 1 approving review is required by reviewers with write access".

[kennethshsu]

Let me check on what's going on...

[andyhufford-HARC]

Did you ever resolve the PR? Also I tried to run with the "daily" grain [approximation_grain='D'] and I couldn't get it to work.

testing CAS example

import chainladder as cl
import pandas as pd

rate_history = pd.DataFrame({
'EffDate': ['2010-07-01', '2011-01-01', '2012-04-01'],
'RateChange': [.05, 0.10, -.01]})
print(rate_history)

data = pd.DataFrame({
'Year': list(range(2005,2015)),
'EarnedPremium': [10_000]*10})

prem_tri = cl.Triangle(data, origin='Year', columns='EarnedPremium')
prem_tri = cl.ParallelogramOLF(rate_history, change_col='RateChange', date_col='EffDate', approximation_grain='D', vertical_line=False).fit_transform(prem_tri)
print(prem_tri.olf_)