Fixes to edge cases in stratify (LR) sample method

src/stv/gregory/mod.rs

@@ -135,7 +135,7 @@ where
 			}
 		};
 		let elected_candidate = if max_cands.len() > 1 {
-			super::choose_highest(state, opts, max_cands, "Which candidate's surplus to distribute?")?
+			super::choose_highest(state, opts, &max_cands, "Which candidate's surplus to distribute?")?
 		} else {
 			max_cands[0]
 		};

src/stv/mod.rs

@@ -1061,7 +1061,7 @@ fn elect_sure_winners<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVOp
 	while !leading_hopefuls.is_empty() && state.num_elected < state.election.seats {
 		let max_cands = ties::multiple_max_by(&leading_hopefuls, |c| &state.candidates[c].votes);
 		let candidate = if max_cands.len() > 1 {
-			choose_highest(state, opts, max_cands, "Which candidate to elect?")?
+			choose_highest(state, opts, &max_cands, "Which candidate to elect?")?
 		} else {
 			max_cands[0]
 		};
@@ -1109,7 +1109,7 @@ fn elect_hopefuls<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVOption
 		// Declare elected in descending order of votes
 		let max_cands = ties::multiple_max_by(&cands_meeting_quota, |c| &state.candidates[c].votes);
 		let candidate = if max_cands.len() > 1 {
-			choose_highest(state, opts, max_cands, "Which candidate to elect?")?
+			choose_highest(state, opts, &max_cands, "Which candidate to elect?")?
 		} else {
 			max_cands[0]
 		};
@@ -1207,7 +1207,7 @@ where
 		if num_to_exclude > 0 {
 			let total_excluded = to_exclude.into_iter()
 				.fold(N::new(), |acc, c| acc + &state.candidates[c].votes);
-			if total_surpluses > &(&hopefuls[num_to_exclude + 1].1.votes - &total_excluded) {
+			if total_surpluses > &(&hopefuls[num_to_exclude].1.votes - &total_excluded) {
 				return false;
 			}
 		}
@@ -1265,7 +1265,7 @@ fn do_bulk_elect<N: Number>(state: &mut CountState<N>, opts: &STVOptions, templa
 	while !hopefuls.is_empty() {
 		let max_cands = ties::multiple_max_by(&hopefuls, |c| &state.candidates[c].votes);
 		let candidate = if max_cands.len() > 1 {
-			choose_highest(state, opts, max_cands, "Which candidate to elect?")?
+			choose_highest(state, opts, &max_cands, "Which candidate to elect?")?
 		} else {
 			max_cands[0]
 		};
@@ -1330,7 +1330,7 @@ where
 			// Exclude only the lowest-ranked doomed candidate
 			let min_cands = ties::multiple_min_by(&doomed, |c| &state.candidates[c].votes);
 			excluded_candidates = if min_cands.len() > 1 {
-				vec![choose_lowest(state, opts, min_cands, "Which candidate to exclude?")?]
+				vec![choose_lowest(state, opts, &min_cands, "Which candidate to exclude?")?]
 			} else {
 				vec![min_cands[0]]
 			};
@@ -1468,7 +1468,7 @@ where
 		
 		let min_cands = ties::multiple_min_by(&hopefuls, |c| &state.candidates[c].votes);
 		excluded_candidates = if min_cands.len() > 1 {
-			vec![choose_lowest(state, opts, min_cands, "Which candidate to exclude?")?]
+			vec![choose_lowest(state, opts, &min_cands, "Which candidate to exclude?")?]
 		} else {
 			vec![min_cands[0]]
 		};
@@ -1586,7 +1586,7 @@ fn finished_before_stage<N: Number>(state: &CountState<N>) -> bool {
 /// Break a tie between the given candidates according to [STVOptions::ties], selecting the highest candidate
 ///
 /// The given candidates are assumed to be tied in this round.
-fn choose_highest<'c, N: Number>(state: &mut CountState<N>, opts: &STVOptions, candidates: Vec<&'c Candidate>, prompt_text: &str) -> Result<&'c Candidate, STVError> {
+pub fn choose_highest<'c, N: Number>(state: &mut CountState<N>, opts: &STVOptions, candidates: &Vec<&'c Candidate>, prompt_text: &str) -> Result<&'c Candidate, STVError> {
 	for strategy in opts.ties.iter() {
 		match strategy.choose_highest(state, opts, &candidates, prompt_text) {
 			Ok(c) => {
@@ -1607,7 +1607,7 @@ fn choose_highest<'c, N: Number>(state: &mut CountState<N>, opts: &STVOptions, c
 /// Break a tie between the given candidates according to [STVOptions::ties], selecting the lowest candidate
 ///
 /// The given candidates are assumed to be tied in this round.
-fn choose_lowest<'c, N: Number>(state: &mut CountState<N>, opts: &STVOptions, candidates: Vec<&'c Candidate>, prompt_text: &str) -> Result<&'c Candidate, STVError> {
+pub fn choose_lowest<'c, N: Number>(state: &mut CountState<N>, opts: &STVOptions, candidates: &Vec<&'c Candidate>, prompt_text: &str) -> Result<&'c Candidate, STVError> {
 	for strategy in opts.ties.iter() {
 		match strategy.choose_lowest(state, opts, &candidates, prompt_text) {
 			Ok(c) => {

src/stv/sample.rs

@@ -188,19 +188,38 @@ where
 				// Round remainders to remove loss by fraction
 				let transferred = candidate_transfers_remainders.values().fold(N::new(), |acc, (t, _)| acc + t);
 				let loss_fraction = &surplus - &transferred;
-				if !loss_fraction.is_zero() {
+				if !loss_fraction.is_zero() && surplus_fraction.is_some() {
 					let n_to_round: usize = format!("{:.0}", loss_fraction).parse().expect("Loss by fraction overflows usize");
 					
-					let mut cands_by_remainder: Vec<Option<&Candidate>> = candidate_transfers_remainders.keys().cloned().collect();
+					let mut cands_by_remainder = candidate_transfers_remainders.keys().cloned().collect::<Vec<_>>();
+					
+					// Sort by whole parts
 					// Compare b to a to sort high-low
-					cands_by_remainder.sort_unstable_by(|a, b| candidate_transfers_remainders[b].1.cmp(&candidate_transfers_remainders[a].1));
+					cands_by_remainder.sort_unstable_by(|a, b| candidate_transfers_remainders[b].0.cmp(&candidate_transfers_remainders[a].0));
+					
+					// Then sort by remainders
+					cands_by_remainder.sort_by(|a, b| candidate_transfers_remainders[b].1.cmp(&candidate_transfers_remainders[a].1));
 					
 					// Select top remainders
-					let top_remainders: Vec<&Option<&Candidate>> = cands_by_remainder.iter().take(n_to_round).collect();
+					let mut top_remainders = cands_by_remainder.iter().take(n_to_round).collect::<Vec<_>>();
 					
 					// Check for tied remainders
-					if candidate_transfers_remainders[top_remainders.last().unwrap()].1 == candidate_transfers_remainders[cands_by_remainder.iter().nth(n_to_round + 1).unwrap()].1 {
+					if candidate_transfers_remainders[top_remainders.last().unwrap()] == candidate_transfers_remainders[cands_by_remainder.iter().nth(n_to_round).unwrap()] {
-						todo!("Tie for largest remainders");
+						// Get the top entry
+						let top_entry = &candidate_transfers_remainders[top_remainders.last().unwrap()];
+						
+						// Separate out tied entries
+						top_remainders = top_remainders.into_iter().filter(|c| &candidate_transfers_remainders[c] != top_entry).collect();
+						let mut tied_top = cands_by_remainder.iter()
+							.filter_map(|c| if let Some(c2) = c { if &candidate_transfers_remainders[c] == top_entry { Some(*c2) } else { None } } else { None })
+							.collect::<Vec<_>>();
+						
+						// Get top entries by tie-breaking method
+						for _ in 0..(n_to_round-top_remainders.len()) {
+							let cand = super::choose_highest(state, opts, &tied_top, "Which fraction to round up?")?;
+							tied_top.remove(tied_top.iter().position(|c| *c == cand).unwrap());
+							top_remainders.push(cands_by_remainder.iter().find(|c| **c == Some(cand)).unwrap());
+						}
 					}
 					
 					// Round up top remainders

src/stv/wasm.rs

@@ -309,7 +309,7 @@ impl STVOptions {
 // Reporting
 
 /// Generate the lead-in description of the count in HTML
-fn describe_count<N: Number>(filename: String, election: &Election<N>, opts: &stv::STVOptions) -> String {
+pub fn describe_count<N: Number>(filename: String, election: &Election<N>, opts: &stv::STVOptions) -> String {
 	let mut result = String::from("<p>Count computed by OpenTally (revision ");
 	result.push_str(crate::VERSION);
 	let total_ballots = election.ballots.iter().fold(N::zero(), |acc, b| { acc + &b.orig_value });
@@ -326,7 +326,7 @@ fn describe_count<N: Number>(filename: String, election: &Election<N>, opts: &st
 }
 
 /// Generate the first column of the HTML results table
-fn init_results_table<N: Number>(election: &Election<N>, opts: &stv::STVOptions, report_style: &str) -> String {
+pub fn init_results_table<N: Number>(election: &Election<N>, opts: &stv::STVOptions, report_style: &str) -> String {
 	let mut result = String::from(r#"<tr class="stage-no"><td rowspan="3"></td></tr><tr class="stage-kind"></tr><tr class="stage-comment"></tr>"#);
 	
 	if report_style == "ballots_votes" {
@@ -361,7 +361,7 @@ fn init_results_table<N: Number>(election: &Election<N>, opts: &stv::STVOptions,
 }
 
 /// Generate subsequent columns of the HTML results table
-fn update_results_table<N: Number>(stage_num: usize, state: &CountState<N>, opts: &stv::STVOptions, report_style: &str) -> Array {
+pub fn update_results_table<N: Number>(stage_num: usize, state: &CountState<N>, opts: &stv::STVOptions, report_style: &str) -> Array {
 	let result = Array::new();
 	
 	// Insert borders to left of new exclusions in Wright STV
@@ -621,7 +621,7 @@ fn update_results_table<N: Number>(stage_num: usize, state: &CountState<N>, opts
 }
 
 /// Get the comment for the current stage
-fn update_stage_comments<N: Number>(state: &CountState<N>, stage_num: usize) -> String {
+pub fn update_stage_comments<N: Number>(state: &CountState<N>, stage_num: usize) -> String {
 	let mut comments = state.logger.render().join(" ");
 	if let Some(_) = state.transfer_table {
 		comments.push_str(&format!(r##" <a href="#" class="detailedTransfersLink" onclick="viewDetailedTransfers({});return false;">[View detailed transfers]</a>"##, stage_num));
@@ -630,7 +630,7 @@ fn update_stage_comments<N: Number>(state: &CountState<N>, stage_num: usize) ->
 }
 
 /// Generate the final column of the HTML results table
-fn finalise_results_table<N: Number>(state: &CountState<N>, report_style: &str) -> Array {
+pub fn finalise_results_table<N: Number>(state: &CountState<N>, report_style: &str) -> Array {
 	let result = Array::new();
 	
 	// Header rows
@@ -673,7 +673,7 @@ fn finalise_results_table<N: Number>(state: &CountState<N>, report_style: &str)
 }
 
 /// Generate the final lead-out text summarising the result of the election
-fn final_result_summary<N: Number>(state: &CountState<N>, opts: &stv::STVOptions) -> String {
+pub fn final_result_summary<N: Number>(state: &CountState<N>, opts: &stv::STVOptions) -> String {
 	let mut result = String::from("<p>Count complete. The winning candidates are, in order of election:</p><ol>");
 	
 	let mut winners = Vec::new();