Merge pull request #717 from ArendPeter/single-surplus

Fix edge case for single fractional surplus

packages/backend/src/Tabulators/AllocatedScore.test.ts

@@ -23,6 +23,48 @@ describe("Allocated Score Tests", () => {
         expect(results.summaryData.weightedScoresByRound[0]).toStrictEqual([25, 24, 24, 23]);  
         expect(results.summaryData.weightedScoresByRound[1]).toStrictEqual([0, 0, 16, 23]);  
     })
+    test("Single vote fractional surplus", () => {
+        // Two winners, two main parties
+        // Allison wins first round with highest score
+        // quota = 4.5
+        // Round 1: Allison's 5 star supporters are weighted to 0, her 4 star supported is weighted to 0.5
+        // Carmen's score is reduced some causing Doug to win second 
+        // Round 2: Doug wins
+        const candidates = ['Allison', 'Bill', 'Carmen', 'Doug']
+        const votes = [
+            [5, 5, 0, 0], // Round 1 Weight Change: 1 -> 0
+            [5, 5, 0, 0], // Round 1 Weight Change: 1 -> 0
+            [5, 5, 0, 0], // Round 1 Weight Change: 1 -> 0
+            [5, 5, 0, 0], // Round 1 Weight Change: 1 -> 0
+            [4, 0, 4, 0], // Round 1 Weight Change: 1 -> 0.5
+            [0, 0, 0, 3],
+            [0, 0, 4, 5],
+            [0, 0, 4, 5],
+            [0, 0, 4, 5],
+        ]
+        const results = AllocatedScore(candidates, votes, 2, [], false, false)
+        expect(results.elected.length).toBe(2);
+        expect(results.elected[0].name).toBe('Allison');
+        expect(results.elected[1].name).toBe('Doug');
+        expect(results.summaryData.weightedScoresByRound[0]).toStrictEqual([24, 20, 16, 18]);  
+        expect(results.summaryData.weightedScoresByRound[1]).toStrictEqual([0, 0, 14, 18]);  
+        expect(results.summaryData.splitPoints[0]).toStrictEqual(0.8);  
+    })
+    test("Voters < Winners", () => {
+        const candidates = ['Allison', 'Bill', 'Carmen', 'Doug']
+        const votes = [
+            [5, 5, 0, 0], 
+            [5, 4, 3, 0], 
+        ]
+        const results = AllocatedScore(candidates, votes, 3, [], false, false)
+        expect(results.elected.length).toBe(3);
+        expect(results.elected[0].name).toBe('Allison');
+        expect(results.elected[1].name).toBe('Bill');
+        expect(results.elected[2].name).toBe('Carmen');
+        expect(results.summaryData.weightedScoresByRound[0]).toStrictEqual([10, 9, 3, 0]);  
+        expect(results.summaryData.weightedScoresByRound[1]).toStrictEqual([0, 6, 2, 0]);  
+        expect(results.summaryData.weightedScoresByRound[2]).toStrictEqual([0, 0, 2, 0]);  
+    })
     test("Fractional surplus", () => {
         // Two winners, two main parties, Allison wins first round with highest score, Allison has 8 highest level supporters, more than the quota of 6 voters
         // Voters who gave Allison their highest score have their ballot weight reduced to (1-6/8) = 0.25

packages/backend/src/Tabulators/AllocatedScore.ts

@@ -144,7 +144,7 @@ export function AllocatedScore(candidates: string[], votes: ballot[], nWinners =
         summaryData.spentAboves.push(spent_above.valueOf());
 
         if (spent_above.valueOf() > 0) {
-            results.logs.push(`The ${rounded(spent_above)} voters who gave ${summaryData.candidates[w].name} more than ${rounded(split_point.mul(maxScore))} stars are fully represented and will be weighted to 0 for future rounds.`)
+            results.logs.push(`The ${rounded(spent_above)} voters who gave ${summaryData.candidates[w].name} more than ${rounded(split_point.mul(maxScore))} stars are fully represented and will be removed from future rounds.`)
             cand_df.forEach((c, i) => {
                 if (c.weighted_score.compare(split_point) > 0) {
                     cand_df[i].ballot_weight = new Fraction(0);
@@ -156,10 +156,9 @@ export function AllocatedScore(candidates: string[], votes: ballot[], nWinners =
 
         // quota = spent_above + weight_on_split*new_weight
         let new_weight = (quota.sub(spent_above)).div(weight_on_split);
-        results.logs.push(`(${rounded(quota)} - ${rounded(spent_above)}) / ${rounded(weight_on_split)} = ${rounded(new_weight)}`)
         results.logs.push(
             `The ${rounded(weight_on_split)} voters who gave ${summaryData.candidates[w].name} ${rounded(split_point.mul(maxScore))} stars are partially represented. `+
-            `${percent(new_weight)} of their vote will go toward ${summaryData.candidates[w].name} and ${percent(new Fraction(1).sub(new_weight))} will be preserved for future rounds.`)
+            `${percent(new_weight)} of their remaining vote will go toward ${summaryData.candidates[w].name} and ${percent(new Fraction(1).sub(new_weight))} will be preserved for future rounds.`)
 
         summaryData.weight_on_splits.push(weight_on_split.valueOf());
         ballot_weights = updateBallotWeights(
@@ -374,17 +373,17 @@ function normalizeArray(scores: ballot[], maxScore: number) {
 }
 
 function findSplitPoint(cand_df_sorted: winner_scores[], quota: typeof Fraction) {
-    var under_quota : any[] = [];
-    var under_quota_scores: typeof Fraction[] = [];
-    var cumsum = new Fraction(0);
-    cand_df_sorted.forEach((c, i) => {
+    let cumsum : typeof Fraction = new Fraction(0);
+    for(const c of cand_df_sorted ){
         cumsum = cumsum.add(c.ballot_weight);
-        if (cumsum < quota || i == 0) {
-            under_quota.push(c);
-            under_quota_scores.push(c.weighted_score);
+
+        // Since cand_df_sorted is sorted by weighted score we know that this will be the smallest
+        if(cumsum.compare(quota) >= 0){
+            return c.weighted_score;
         }
-    });
-    return findMinFrac(under_quota_scores);
+    }
+
+    return cand_df_sorted.slice(-1)[0].weighted_score
 }
 
 function sortMatrix(matrix: number[][], order: number[]) {
@@ -398,14 +397,4 @@ function sortMatrix(matrix: number[][], order: number[]) {
         });
     });
     return newMatrix
-}
-
-function findMinFrac(fracs: typeof Fraction[]) {
-    let minFrac = fracs[0]
-    fracs.forEach(frac => {
-        if (frac.compare(minFrac) < 0) {
-            minFrac = frac
-        }
-    })
-    return minFrac
-}
+}

packages/backend/src/Tabulators/ParseData.ts

@@ -37,9 +37,6 @@ module.exports = function ParseData(data: ballot[], validityCheck = getStarBallo
         }
         else if (ballotValidity.isUnderVote) {
             underVotes += 1
-            scores.push(row)
-            // under votes should not count as a valid vote
-            //validVotes.push(voter);
         }
         else {
             scores.push(row)

packages/frontend/src/components/Election/Results/Results.tsx

@@ -398,12 +398,11 @@ function PRResultsViewer() {
     </WidgetContainer>
     <DetailExpander>
       <WidgetContainer>
-      <Widget title={t('results.star_pr.table_title')} wide>
-        <ResultsTable className='starPRTable' data={tabulationRows}/>
-      </Widget>
+        <Widget title={t('results.star_pr.table_title')} wide>
+          <ResultsTable className='starPRTable' data={tabulationRows}/>
+        </Widget>
       </WidgetContainer>
       <WidgetContainer>
-      {flags.isSet('ALL_STATS') &&
         <Widget title={t('results.star.detailed_steps_title')} wide>
           <div className='detailedSteps'>
             <ol style={{textAlign: 'left'}}>
@@ -413,7 +412,6 @@ function PRResultsViewer() {
             </ol>
           </div>
         </Widget>
-      }
       </WidgetContainer>
       <DetailExpander level={1}>
         <WidgetContainer>