Midterms: House seat-distribution → discrete chart + Medalists CP by aseckin · Pull Request #4868 · Metaculus/metaculus

aseckin · 2026-06-09T15:09:01Z

Builds on the merged 2026 US Midterms dashboard. Two coupled changes to the Seat Distribution section.

Changes

House seat-distribution rendered as a discrete chart

The House question was converted from Continuous to Discrete (like the Senate). The chart now derives its bars from each question's native discrete outcomes (getDiscreteValueOptions) and buckets the PMF by bin index, instead of integer-rounding the raw range. The Senate renders identically (25 bars, -12…+12); the House renders its 81 native bars (-40…+40) from its 201-point CDF, with no phantom edge bin.
Landslide tails kept: the open-bound mass is folded into the edge bins, so a result beyond the chart range (e.g. Democrats winning the House by 40+ seats) is represented at the edge rather than dropped — bars sum to ~100%. (The resulting edge spike is handled on the data side.)
EVEN label moved above the even bin with a short connector line and an inverted, background-readable color (the old on-bar white was illegible on the House's thin bars).

Medalists CP

Both seat-distribution charts now show the Medalists community prediction, fetched by reusing ServerAggregationsExplorerApi.getAggregations({ aggregationMethods: "medalists" }) — no new aggregation logic, no backend change. The chart takes a cdfOverride prop; fetchSeatDistributions returns the post + the Medalists CDF. No community fallback — if Medalists is empty, the section shows the existing "unavailable" placeholder.

🤖 Generated with Claude Code

Summary by CodeRabbit

New Features
- Seat distribution charts now support a CDF override and can display Medalists aggregation CDFs when available.
- Seat distribution dashboard slots use enriched data and show an “unavailable” placeholder if charts/Medalists CDF data is missing.
Bug Fixes
- Discrete chart rendering, tick placement, and out-of-bounds tooltip/label behavior were improved, including “over {count} seats” tooltip text across locales.
- EVEN annotation geometry and connector rendering were refined; discrete hover targeting was updated to avoid connector/divider elements.
Documentation
- Updated seat-advantage chart descriptions to reflect discrete (integer-spaced) signed distributions for both questions.

Task 1 (discrete House): derive the discrete chart's bars from the question's native outcomes (getDiscreteValueOptions) and bucket the PMF by bin index, instead of integer-rounding the raw range. The Senate renders identically (25 bars, -12..+12); the now-discrete House renders its 81 native bars (-40..+40) from its 201-point CDF, with no phantom edge bin. Task 2 (Medalists CP): both seat-distribution charts show the Medalists community prediction, fetched by reusing ServerAggregationsExplorerApi (/aggregation_explorer/, method=medalists). fetchSeatDistributions returns the post + the Medalists CDF; the chart takes a `cdfOverride` prop. No community fallback -- if Medalists is empty, the section shows the existing "unavailable" placeholder. Validated against the live project: Senate distribution centers on even, House on ~D+10; both render as native-bin discrete bars. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

- Fold the open-bound mass into the edge bins so a landslide beyond the chart range (e.g. Democrats winning the House by 40+) is represented at the edge instead of dropped; bars now sum to ~100%. - Move the EVEN label above the bin with a short connector line (~8px, darker than the gray bin) and invert its color to read on the chart background. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

coderabbitai · 2026-06-09T15:09:09Z

Note

Reviews paused

It looks like this branch is under active development. To avoid overwhelming you with review comments due to an influx of new commits, CodeRabbit has automatically paused this review. You can configure this behavior by changing the reviews.auto_review.auto_pause_after_reviewed_commits setting.

Use the following commands to manage reviews:

@coderabbitai resume to resume automatic reviews.
@coderabbitai review to trigger a single review.

Use the checkboxes below for quick actions:

▶️ Resume reviews
✅ Review completed - (🔄 Check again to review again)

📝 Walkthrough

Walkthrough

Fetches medalists aggregation CDFs, returns enriched SeatDistributionDatum, passes datum to the section, wires a cdfOverride prop into SeatDistributionChart, and refactors discrete-mode rendering plus EVEN annotation geometry and tooltip blacklisting.

Changes

Medalists CDF override feature

Layer / File(s)	Summary
Data contract and medalists CDF fetching `front_end/src/app/(main)/midterms-2026/helpers/fetch_dashboard_data.ts`, `front_end/src/app/(main)/midterms-2026/data.ts`	Defines `SeatDistributionDatum` combining `post` and `medalistsCdf`. Updates `fetchSeatDistributions` to fetch posts and medalists aggregation CDFs concurrently via `ServerAggregationsExplorerApi`, returning null-safe datum objects. Updates house post id and docs.
Section integration with datum prop `front_end/src/app/(main)/midterms-2026/sections/seat_distributions.tsx`	Refactors `SeatDistributionsSection` and `DistributionSlot` to accept `datum: SeatDistributionDatum
Chart CDF prop wiring and imports `front_end/src/app/(main)/midterms-2026/components/seat_distribution_chart.tsx`	Adds `cdfOverride?: number[]`, imports `getDiscreteValueOptions`, threads `cdfOverride` into props and useMemo dependencies, and selects CDF with `cdfOverride ?? defaultCdf`.
Discrete distribution construction & tooltips `front_end/src/app/(main)/midterms-2026/components/seat_distribution_chart.tsx`	Discrete mode now derives bins from native outcome options and PMF masses (including edge sentinels), validates PMF resolution against bins, and stops building continuous house tooltip points; Voronoi blacklist updated for discrete mode.
Axis ticks and EVEN annotation geometry/rendering `front_end/src/app/(main)/midterms-2026/components/seat_distribution_chart.tsx`	X-axis tick computation is refactored to sample discrete bin x-values and include x=0 when present; edge labels use `≤`/`≥`. EVEN connector length and pixel geometry recalculated, discrete EVEN rendered as a `VictoryLine` connector plus `VictoryLabel`, and connector excluded from voronoi tooltips.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

Metaculus/metaculus#4844: Overlaps SeatDistributionChart’s VictoryVoronoiContainer adjustments (tooltip/voronoi behavior).

Suggested reviewers

ncarazon
lsabor
elisescu

Poem

🐰 I fetched the medalists' CDF with care,
I threaded datum through the chart's thin air,
Discrete bins aligned and tails folded neat,
EVEN now connects, a tidy little feat,
A rabbit hops — the visualization's sweet.

🚥 Pre-merge checks | ✅ 4

✅ 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 accurately identifies the two main changes: converting House seat-distribution to a discrete chart and integrating Medalists community prediction, matching the primary scope of the PR.
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.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

Create PR with unit tests
Commit unit tests in branch midterm-followups-2

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

coderabbitai

🧹 Nitpick comments (1)

front_end/src/app/(main)/midterms-2026/helpers/fetch_dashboard_data.ts (1)
278-291: Downgrade the runtime type-guard suggestion for medalists seat distributions

ServerAggregationsExplorerApi.getAggregations returns a union (AggregationExtraQuestion), so the as NumericAggregationExtraQuestion cast still narrows without checks. However, postId for this call is sourced only from SEAT_DISTRIBUTION_POSTS (discrete/continuous numeric seat-distribution questions) and SeatDistributionChart also assumes post.question is QuestionWithNumericForecasts, so the cast should match reality here. An explicit guard is still optional if you want future-proofing (e.g., check question.type !== QuestionType.MultipleChoice or ensure aggregations.medalists.latest.forecast_values exists before reading).
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@front_end/src/app/`(main)/midterms-2026/helpers/fetch_dashboard_data.ts
around lines 278 - 291, fetchMedalistsCdf currently force-casts the result of
ServerAggregationsExplorerApi.getAggregations to NumericAggregationExtraQuestion
which narrows without runtime checks; update fetchMedalistsCdf so it still
returns the medalists forecast_values safely by verifying the path exists before
returning (check question?.aggregations?.medalists?.latest?.forecast_values or
guard question.type !== QuestionType.MultipleChoice) instead of relying only on
the as NumericAggregationExtraQuestion cast, and keep returning null on failure;
reference ServerAggregationsExplorerApi.getAggregations,
NumericAggregationExtraQuestion, and fetchMedalistsCdf to locate the change.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@front_end/src/app/`(main)/midterms-2026/helpers/fetch_dashboard_data.ts:
- Around line 278-291: fetchMedalistsCdf currently force-casts the result of
ServerAggregationsExplorerApi.getAggregations to NumericAggregationExtraQuestion
which narrows without runtime checks; update fetchMedalistsCdf so it still
returns the medalists forecast_values safely by verifying the path exists before
returning (check question?.aggregations?.medalists?.latest?.forecast_values or
guard question.type !== QuestionType.MultipleChoice) instead of relying only on
the as NumericAggregationExtraQuestion cast, and keep returning null on failure;
reference ServerAggregationsExplorerApi.getAggregations,
NumericAggregationExtraQuestion, and fetchMedalistsCdf to locate the change.

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: f63168aa-bc73-4ae2-8141-9e357c323dfc

📥 Commits

Reviewing files that changed from the base of the PR and between 0e91c1a and 72ea520.

📒 Files selected for processing (3)

front_end/src/app/(main)/midterms-2026/components/seat_distribution_chart.tsx
front_end/src/app/(main)/midterms-2026/helpers/fetch_dashboard_data.ts
front_end/src/app/(main)/midterms-2026/sections/seat_distributions.tsx

github-actions · 2026-06-09T15:20:09Z

🚀 Preview Environment

Your preview environment is ready!

Resource	Details
🌐 Preview URL	https://metaculus-pr-4868-midterm-followups-2-preview.mtcl.cc
📦 Docker Image	`ghcr.io/metaculus/metaculus:midterm-followups-2-9a34847`
🗄️ PostgreSQL	NeonDB branch `preview/pr-4868-midterm-followups-2`
⚡ Redis	Fly Redis `mtc-redis-pr-4868-midterm-followups-2`

Details

Commit: 39d44cd32885e8abdbffd39d633239b17d8daab6
Branch: midterm-followups-2
Fly App: metaculus-pr-4868-midterm-followups-2

ℹ️ Preview Environment Info

Isolation:

PostgreSQL and Redis are fully isolated from production
Each PR gets its own database branch and Redis instance
Changes pushed to this PR will trigger a new deployment

Limitations:

Background workers and cron jobs are not deployed in preview environments
If you need to test background jobs, use Heroku staging environments

Cleanup:

This preview will be automatically destroyed when the PR is closed

Pin the leftmost/rightmost x-axis ticks to the integer bin extremes (ceil(rangeMin) / floor(rangeMax)) instead of rounding the half-integer range bounds. Math.round sends +-X.5 toward +inf (e.g. -39.5 -> -39 but +39.5 -> +40), which produced asymmetric edges; the edges now read -39 / +39 (and the Senate -12 / +12 instead of -12 / +13). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

- Replace the forbidden non-null assertion in the discrete tick sampling with a type-narrowing filter (the @typescript-eslint/no-non-null-assertion error failing the Frontend check). - Move the new discrete House question id (43900) into SEAT_DISTRIBUTION_POSTS in data.ts instead of a hardcoded override beside a commented-out line in the fetch helper; refresh the stale comment (both questions are Discrete now). - Guard the discrete bin mapping: it indexes the PMF 1:1 into native bins, so if a question ever serves a finer-resolution CDF (like the original continuous House question), render the unavailable placeholder instead of silently wrong bars. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

For the House chart only (gated by a new `separateOutOfBounds` prop on the section's House slot): - Push the two open-bound sentinel bins (the first/last entries, identified from the live config — x < range_min / x > range_max — not hardcoded) outward to open a gap, with a thin vertical divider line in each gap (a VictoryLine like the EVEN connector, excluded from the tooltip voronoi). Layout reads gap -> line -> gap -> bin on each side. - Relabel those bins ">N seat advantage" in the tooltip (N = round(range_max)), replacing the incorrect rounded value (e.g. "41"). New i18n key midtermsHubSeatAdvantageOverTooltip across 6 locales. The Senate is untouched (gate off). Gap size (OOB_GAP_STEPS) and divider style are tunable for iteration. Verified the target config (-40..40, 40 outcomes) by simulation: odd-int bins -39..39, OOB pushed to +-43, dividers at +-41, guard passes, OOB tooltips resolve to ">40 seat advantage". Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

The OOB divider lines now span 50% of the chart's vertical height instead of the full height (new tunable OOB_DIVIDER_HEIGHT_FRAC = 0.5). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

coderabbitai

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

front_end/src/app/(main)/midterms-2026/sections/seat_distributions.tsx (1)
76-76: ⚠️ Potential issue | 🟡 Minor | ⚡ Quick win

Align the Medalists CDF validity guard with the chart contract.

Line 76 treats any non-empty medalistsCdf as valid, but SeatDistributionChart rejects CDFs with length < 2; that can produce a blank slot instead of the unavailable placeholder.
Suggested fix
-  if (!datum || !datum.medalistsCdf?.length) {
+  if (!datum || (datum.medalistsCdf?.length ?? 0) < 2) {
🤖 Prompt for AI Agents
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@front_end/src/app/`(main)/midterms-2026/sections/seat_distributions.tsx at
line 76, The validity guard on line 76 checks if medalistsCdf is non-empty, but
SeatDistributionChart requires a minimum length of 2 for the CDF to be valid.
Update the condition from checking !datum.medalistsCdf?.length to checking that
medalistsCdf?.length is greater than or equal to 2, so that CDFs with length 1
are treated as invalid and trigger the unavailable placeholder instead of
passing through to SeatDistributionChart which will then reject them and create
a blank slot.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Outside diff comments:
In `@front_end/src/app/`(main)/midterms-2026/sections/seat_distributions.tsx:
- Line 76: The validity guard on line 76 checks if medalistsCdf is non-empty,
but SeatDistributionChart requires a minimum length of 2 for the CDF to be
valid. Update the condition from checking !datum.medalistsCdf?.length to
checking that medalistsCdf?.length is greater than or equal to 2, so that CDFs
with length 1 are treated as invalid and trigger the unavailable placeholder
instead of passing through to SeatDistributionChart which will then reject them
and create a blank slot.

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: a88b0db8-3456-4f1a-b3ba-e9c7c9cfdc7f

📥 Commits

Reviewing files that changed from the base of the PR and between c810ab5 and 1744f96.

📒 Files selected for processing (10)

front_end/messages/cs.json
front_end/messages/en.json
front_end/messages/es.json
front_end/messages/pt.json
front_end/messages/zh-TW.json
front_end/messages/zh.json
front_end/src/app/(main)/midterms-2026/components/seat_distribution_chart.tsx
front_end/src/app/(main)/midterms-2026/data.ts
front_end/src/app/(main)/midterms-2026/helpers/fetch_dashboard_data.ts
front_end/src/app/(main)/midterms-2026/sections/seat_distributions.tsx

✅ Files skipped from review due to trivial changes (5)

front_end/messages/pt.json
front_end/messages/en.json
front_end/messages/es.json
front_end/messages/cs.json
front_end/src/app/(main)/midterms-2026/data.ts

🚧 Files skipped from review as they are similar to previous changes (2)

front_end/src/app/(main)/midterms-2026/helpers/fetch_dashboard_data.ts
front_end/src/app/(main)/midterms-2026/components/seat_distribution_chart.tsx

Align the section's availability check with SeatDistributionChart's own minimum (cdf.length < 2 -> null): a degenerate 1-point Medalists CDF now shows the "unavailable" placeholder instead of slipping through to a blank slot. Phrased as `!datum?.medalistsCdf || length < 2` to preserve the non-null narrowing the cdfOverride prop relies on. Addresses PR review feedback. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

aseckin and others added 2 commits June 9, 2026 15:13

Merge branch 'main' into midterm-followups-2

72ea520

aseckin marked this pull request as ready for review June 9, 2026 15:09

aseckin temporarily deployed to testing_env June 9, 2026 15:09 — with GitHub Actions Inactive

aseckin requested a review from ncarazon June 9, 2026 15:09

aseckin temporarily deployed to Preview June 9, 2026 15:17 — with GitHub Actions Inactive

coderabbitai Bot reviewed Jun 9, 2026

View reviewed changes

ncarazon approved these changes Jun 9, 2026

View reviewed changes

lsabor temporarily deployed to dev_env June 10, 2026 18:57 — with GitHub Actions Inactive

aseckin had a problem deploying to testing_env June 11, 2026 06:48 — with GitHub Actions Error

aseckin temporarily deployed to testing_env June 11, 2026 06:48 — with GitHub Actions Inactive

Merge branch 'main' into midterm-followups-2

232d79e

aseckin temporarily deployed to testing_env June 11, 2026 06:51 — with GitHub Actions Inactive

aseckin temporarily deployed to Preview June 11, 2026 06:59 — with GitHub Actions Inactive

aseckin temporarily deployed to dev_env June 11, 2026 07:00 — with GitHub Actions Inactive

fix discrete chart

9d3930e

lsabor temporarily deployed to testing_env June 11, 2026 16:42 — with GitHub Actions Inactive

lsabor temporarily deployed to Preview June 11, 2026 16:50 — with GitHub Actions Inactive

update ticks to only choose from bucket centers

c810ab5

lsabor temporarily deployed to testing_env June 11, 2026 16:55 — with GitHub Actions Inactive

lsabor temporarily deployed to Preview June 11, 2026 17:03 — with GitHub Actions Inactive

Merge branch 'main' into midterm-followups-2

5fb4115

aseckin temporarily deployed to testing_env June 12, 2026 12:30 — with GitHub Actions Inactive

aseckin temporarily deployed to Preview June 12, 2026 12:38 — with GitHub Actions Inactive

lsabor reviewed Jun 12, 2026

View reviewed changes

Comment thread front_end/src/app/(main)/midterms-2026/data.ts

restore previous post id

daedc8d

lsabor had a problem deploying to testing_env June 12, 2026 15:35 — with GitHub Actions Error

lsabor temporarily deployed to testing_env June 12, 2026 15:35 — with GitHub Actions Inactive

update claude comment

2320da0

lsabor temporarily deployed to testing_env June 12, 2026 15:40 — with GitHub Actions Inactive

lsabor temporarily deployed to testing_env June 12, 2026 15:41 — with GitHub Actions Inactive

lsabor temporarily deployed to Preview June 12, 2026 15:49 — with GitHub Actions Inactive

lsabor temporarily deployed to dev_env June 12, 2026 15:55 — with GitHub Actions Inactive

github-actions Bot temporarily deployed to Preview June 14, 2026 08:24 Inactive

aseckin temporarily deployed to testing_env June 16, 2026 22:49 — with GitHub Actions Inactive

aseckin temporarily deployed to Preview June 16, 2026 22:57 — with GitHub Actions Inactive

aseckin temporarily deployed to dev_env June 16, 2026 22:57 — with GitHub Actions Inactive

Midterms House seat-dist: half-height out-of-bounds divider lines

1744f96

The OOB divider lines now span 50% of the chart's vertical height instead of the full height (new tunable OOB_DIVIDER_HEIGHT_FRAC = 0.5). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

aseckin temporarily deployed to testing_env June 16, 2026 23:14 — with GitHub Actions Inactive

aseckin temporarily deployed to Preview June 16, 2026 23:21 — with GitHub Actions Inactive

aseckin temporarily deployed to dev_env June 16, 2026 23:26 — with GitHub Actions Inactive

coderabbitai Bot reviewed Jun 16, 2026

View reviewed changes

aseckin temporarily deployed to testing_env June 16, 2026 23:36 — with GitHub Actions Inactive

aseckin deployed to Preview June 16, 2026 23:44 — with GitHub Actions View deployment

aseckin deployed to dev_env June 16, 2026 23:50 — with GitHub Actions Active

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Midterms: House seat-distribution → discrete chart + Medalists CP#4868

Midterms: House seat-distribution → discrete chart + Medalists CP#4868
aseckin wants to merge 14 commits into
mainfrom
midterm-followups-2

aseckin commented Jun 9, 2026 •

edited by coderabbitai Bot

Loading

Uh oh!

coderabbitai Bot commented Jun 9, 2026 •

edited

Loading

Reviews paused

Walkthrough

Changes

Estimated code review effort

Possibly related PRs

Suggested reviewers

Poem

Uh oh!

coderabbitai Bot left a comment

Uh oh!

github-actions Bot commented Jun 9, 2026 •

edited

Loading

Uh oh!

Uh oh!

coderabbitai Bot left a comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Conversation

aseckin commented Jun 9, 2026 • edited by coderabbitai Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Changes

Summary by CodeRabbit

Uh oh!

coderabbitai Bot commented Jun 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Reviews paused

Walkthrough

Changes

Estimated code review effort

Possibly related PRs

Suggested reviewers

Poem

Uh oh!

coderabbitai Bot left a comment

Choose a reason for hiding this comment

Uh oh!

github-actions Bot commented Jun 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🚀 Preview Environment

Details

Uh oh!

Uh oh!

coderabbitai Bot left a comment

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

aseckin commented Jun 9, 2026 •

edited by coderabbitai Bot

Loading

coderabbitai Bot commented Jun 9, 2026 •

edited

Loading

github-actions Bot commented Jun 9, 2026 •

edited

Loading