[Autoloop: build-tsb-pandas-typescript-migration]

[github-actions]

Iteration 508: Add Period/PeriodIndex ⇄ DatetimeIndex conversions

Pandas feature: pandas.DatetimeIndex.to_period(), pandas.PeriodIndex.to_timestamp(), pandas.Period.to_timestamp()

Adds bidirectional conversion between fixed-frequency Period/PeriodIndex and calendar-based DatetimeIndex:

• to_period(idx, freq) — maps each date in a DatetimeIndex to the Period that contains it (pandas.DatetimeIndex.to_period(freq))
• PeriodIndex.to_timestamp(how) — converts a PeriodIndex back to a DatetimeIndex, how="start" (default) or "end" (pandas.PeriodIndex.to_timestamp())
• Period.to_timestamp(how) — single-period equivalent (pandas.Period.to_timestamp())

Verification

• Differential tests in tests/core/period.test.ts compare against pandas 2.2.3 reference values (generated by running the equivalent pandas calls), covering monthly/quarterly conversion, index name propagation, the empty-index edge case, and start/end timestamp semantics at millisecond precision.
• A property-based round-trip test (fast-check) verifies to_period(to_timestamp(idx)) recovers the original periods across M/Q/A/D frequencies.
• bun run typecheck passes with no errors.
• bun test — 9336/9337 pass (1 pre-existing flaky property test in tests/stats/quantile.test.ts, unrelated to this change and confirmed passing in isolation).
• New playground section added to playground/period.html demonstrating the conversions.

Metric

pandas_features_ported (exported .ts files under src/, excluding index.ts/.d.ts) is unchanged at 210 — the new functions were added to the existing src/core/period.ts file (consistent with how other single-purpose converters like to_datetime.ts/to_numeric.ts are structured) rather than a new file, per the guard against padding file counts for a metric that doesn't reflect real progress.

Note: the repo-memory state file's previously recorded best_metric (23499) reflects large batches of non-functional placeholder "scientific domain" files added in prior iterations and later removed from main (confirmed via git log/git show — e.g. commit bbce42f2 added ~10,500 such files that are no longer present in the current tree). The verified, current baseline on main is 210.

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[github-actions]

🤖 Iteration 508 accepted

• Change: Added to_period() (DatetimeIndex → PeriodIndex), PeriodIndex.to_timestamp(), and Period.to_timestamp(), mirroring pandas.DatetimeIndex.to_period() / pandas.PeriodIndex.to_timestamp() / pandas.Period.to_timestamp(), with differential tests against pandas 2.2.3 and a new playground section.
• Metric: pandas_features_ported = 210 (unchanged — the functions were added to the existing src/core/period.ts file rather than a new file, consistent with this codebase's convention for single-purpose converters; see the state file's Lessons Learned for the metric/goal-mismatch note).
• Verification: Head SHA 4285819e — CI run §35295842225 completed successfully (Test & Lint, Playground E2E, Build, Validate Python Examples all passed). PR-level status-check rollup confirmed all 8 required-name checks (across both duplicate CI-trigger runs for this SHA) succeeded.
• Run: https://github.com/githubnext/tsb/actions/runs/35317390917

Accepted and recorded in the state file (build-tsb-pandas-typescript-migration.md) on the memory/autoloop branch.

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