perf(interaction): look up axis values by key and binary search

[andersk]

Scale-bound interactions with explicit values scanned every value on each pointer event: indexOf searched the array of value keys, and valueAt measured the distance to every position. A brushX over 120,000 hourly values spent about 12 ms per mouse move in these scans, enough to make dragging stutter.

Record each value's index in the map that already checks values for uniqueness, and find the nearest position by binary search, which assertMonotonePositions already makes valid. Ties still resolve to the lower index, as with the linear search.

Summary by CodeRabbit

• Performance
  • Improved pointer snapping and value lookups for charts with many explicitly defined values, including brush, zoom, handle, and cursor interactions.
  • Preserved consistent snapping behavior for forward and reversed axes, including when a pointer falls equally between two values.

[changeset-bot]

🦋 Changeset detected

Latest commit: d73c50c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
@tanstack/charts	Patch
@tanstack/alpine-charts	Patch
@tanstack/angular-charts	Patch
@tanstack/lit-charts	Patch
@tanstack/octane-charts	Patch
@tanstack/preact-charts	Patch
@tanstack/react-charts	Patch
@tanstack/react-native-charts	Patch
@tanstack/solid-charts	Patch
@tanstack/svelte-charts	Patch
@tanstack/vue-charts	Patch
@tanstack/charts-scales	Patch

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between e6a51a8 and d73c50c.

📒 Files selected for processing (3)

• .changeset/interaction-axis-lookups.md
• packages/charts-core/src/interaction-axis-internal.test.ts
• packages/charts-core/src/interaction-axis-internal.ts

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📝 Walkthrough

Walkthrough

The interaction axis now maps explicit values to indexes and uses binary search to select the nearest mapped position. Tests cover forward and reversed mappings, ties, and present or absent values.

Changes

Interaction axis lookups

Layer / File(s)	Summary
Explicit-value index packages/charts-core/src/interaction-axis-internal.ts	The axis builds a key-to-index map while validating explicit values. indexOf uses the map and returns -1 for absent values.
Nearest-position search packages/charts-core/src/interaction-axis-internal.ts, packages/charts-core/src/interaction-axis-internal.test.ts, .changeset/interaction-axis-lookups.md	Explicit-value snapping uses binary search for ascending and descending positions. Tests cover nearest-value selection, endpoint clamping, ties, and indexOf. The changeset records a patch for @tanstack/charts.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to d73c5

No issue requiring a fix before merge is identified for the interaction-axis lookup change.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files. (1 skipped: 1…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: faster interaction-axis lookups by key and binary search.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files. (1 skipped: 1 unsupported.)

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