Implement forwards and backwards tie-breaking

src/election.rs

@@ -131,6 +131,9 @@ pub struct CountState<'a, N> {
 	pub exhausted: CountCard<'a, N>,
 	pub loss_fraction: CountCard<'a, N>,
 	
+	pub forwards_tiebreak: Option<HashMap<&'a Candidate, usize>>,
+	pub backwards_tiebreak: Option<HashMap<&'a Candidate, usize>>,
+	
 	pub quota: Option<N>,
 	pub vote_required_election: Option<N>,
 	
@@ -149,6 +152,8 @@ impl<'a, N: Number> CountState<'a, N> {
 			candidates: HashMap::new(),
 			exhausted: CountCard::new(),
 			loss_fraction: CountCard::new(),
+			forwards_tiebreak: None,
+			backwards_tiebreak: None,
 			quota: None,
 			vote_required_election: None,
 			num_elected: 0,

src/main.rs

@@ -104,6 +104,10 @@ struct STV {
 	// ------------------
 	// -- STV variants --
 	
+	/// Tie-breaking method
+	#[clap(help_heading=Some("STV VARIANTS"), short='t', long, possible_values=&["forwards", "backwards", "random", "prompt"], default_value="prompt", value_name="methods")]
+	ties: Vec<String>,
+	
 	/// Method of surplus distributions
 	#[clap(help_heading=Some("STV VARIANTS"), short='s', long, possible_values=&["wig", "uig", "eg", "meek"], default_value="wig", value_name="method")]
 	surplus: String,
@@ -187,6 +191,7 @@ where
 		&cmd_opts.quota,
 		&cmd_opts.quota_criterion,
 		&cmd_opts.quota_mode,
+		&cmd_opts.ties,
 		&cmd_opts.surplus,
 		&cmd_opts.surplus_order,
 		cmd_opts.transferable_only,

src/stv/mod.rs

@@ -31,8 +31,7 @@ use std::cmp::max;
 use std::collections::HashMap;
 use std::ops;
 
-#[wasm_bindgen]
+pub struct STVOptions<'o> {
-pub struct STVOptions {
 	pub round_tvs: Option<usize>,
 	pub round_weights: Option<usize>,
 	pub round_votes: Option<usize>,
@@ -42,6 +41,7 @@ pub struct STVOptions {
 	pub quota: QuotaType,
 	pub quota_criterion: QuotaCriterion,
 	pub quota_mode: QuotaMode,
+	pub ties: Vec<TieStrategy<'o>>,
 	pub surplus: SurplusMethod,
 	pub surplus_order: SurplusOrder,
 	pub transferable_only: bool,
@@ -51,8 +51,7 @@ pub struct STVOptions {
 	pub pp_decimals: usize,
 }
 
-#[wasm_bindgen]
+impl<'o> STVOptions<'o> {
-impl STVOptions {
 	pub fn new(
 		round_tvs: Option<usize>,
 		round_weights: Option<usize>,
@@ -63,6 +62,7 @@ impl STVOptions {
 		quota: &str,
 		quota_criterion: &str,
 		quota_mode: &str,
+		ties: &Vec<String>,
 		surplus: &str,
 		surplus_order: &str,
 		transferable_only: bool,
@@ -100,6 +100,13 @@ impl STVOptions {
 				"ers97" => QuotaMode::ERS97,
 				_ => panic!("Invalid --quota-mode"),
 			},
+			ties: ties.into_iter().map(|t| match t.as_str() {
+				"forwards" => TieStrategy::Forwards,
+				"backwards" => TieStrategy::Backwards,
+				"random" => todo!(),
+				"prompt" => TieStrategy::Prompt,
+				_ => panic!("Invalid --ties"),
+			}).collect(),
 			surplus: match surplus {
 				"wig" => SurplusMethod::WIG,
 				"uig" => SurplusMethod::UIG,
@@ -124,19 +131,18 @@ impl STVOptions {
 			pp_decimals,
 		};
 	}
-}
+	
-
-impl STVOptions {
-	// Not exported to WebAssembly
 	pub fn describe<N: Number>(&self) -> String {
 		let mut flags = Vec::new();
-		let n_str = N::describe_opt(); if n_str.len() > 0 { flags.push(N::describe_opt()) };
+		let n_str = N::describe_opt(); if !n_str.is_empty() { flags.push(N::describe_opt()) };
 		if let Some(dps) = self.round_tvs { flags.push(format!("--round-tvs {}", dps)); }
 		if let Some(dps) = self.round_weights { flags.push(format!("--round-weights {}", dps)); }
 		if let Some(dps) = self.round_votes { flags.push(format!("--round-votes {}", dps)); }
 		if let Some(dps) = self.round_quota { flags.push(format!("--round-quota {}", dps)); }
 		if self.sum_surplus_transfers != SumSurplusTransfersMode::SingleStep { flags.push(self.sum_surplus_transfers.describe()); }
 		if self.normalise_ballots { flags.push("--normalise-ballots".to_string()); }
+		let ties_str = self.ties.iter().map(|t| t.describe()).join(" ");
+		if ties_str != "prompt" { flags.push(format!("--ties {}", ties_str)); }
 		if self.quota != QuotaType::DroopExact { flags.push(self.quota.describe()); }
 		if self.quota_criterion != QuotaCriterion::Greater { flags.push(self.quota_criterion.describe()); }
 		if self.quota_mode != QuotaMode::Static { flags.push(self.quota_mode.describe()); }
@@ -286,12 +292,14 @@ impl ExclusionMethod {
 #[derive(Debug)]
 pub enum STVError {
 	RequireInput,
+	UnresolvedTie,
 }
 
 pub fn count_init<N: Number>(mut state: &mut CountState<'_, N>, opts: &STVOptions) {
 	distribute_first_preferences(&mut state);
 	calculate_quota(&mut state, opts);
 	elect_meeting_quota(&mut state, opts);
+	init_tiebreaks(&mut state, opts);
 }
 
 pub fn count_one_stage<'a, N: Number>(mut state: &mut CountState<'a, N>, opts: &STVOptions) -> Result<bool, STVError>
@@ -312,6 +320,7 @@ where
 	if continue_exclusion(&mut state, &opts) {
 		calculate_quota(&mut state, opts);
 		elect_meeting_quota(&mut state, opts);
+		update_tiebreaks(&mut state, opts);
 		return Ok(false);
 	}
 	
@@ -319,11 +328,12 @@ where
 	if distribute_surpluses(&mut state, &opts)? {
 		calculate_quota(&mut state, opts);
 		elect_meeting_quota(&mut state, opts);
+		update_tiebreaks(&mut state, opts);
 		return Ok(false);
 	}
 	
 	// Attempt bulk election
-	if bulk_elect(&mut state) {
+	if bulk_elect(&mut state, &opts)? {
 		return Ok(false);
 	}
 	
@@ -331,6 +341,7 @@ where
 	if exclude_hopefuls(&mut state, &opts)? {
 		calculate_quota(&mut state, opts);
 		elect_meeting_quota(&mut state, opts);
+		update_tiebreaks(&mut state, opts);
 		return Ok(false);
 	}
 	
@@ -562,9 +573,9 @@ fn elect_meeting_quota<N: Number>(state: &mut CountState<N>, opts: &STVOptions)
 		.filter(|c| { let cc = state.candidates.get(c).unwrap(); cc.state == CandidateState::Hopeful && meets_quota(vote_req, cc, opts) })
 		.collect();
 	
-	if cands_meeting_quota.len() > 0 {
+	if !cands_meeting_quota.is_empty() {
 		// Sort by votes
-		cands_meeting_quota.sort_unstable_by(|a, b| state.candidates.get(a).unwrap().votes.partial_cmp(&state.candidates.get(b).unwrap().votes).unwrap());
+		cands_meeting_quota.sort_unstable_by(|a, b| state.candidates.get(a).unwrap().votes.cmp(&state.candidates.get(b).unwrap().votes));
 		
 		// Declare elected in descending order of votes
 		for candidate in cands_meeting_quota.into_iter().rev() {
@@ -634,7 +645,7 @@ where
 	let total_surpluses = has_surplus.iter()
 		.fold(N::new(), |acc, (_, cc)| acc + &cc.votes - quota);
 		
-	if has_surplus.len() > 0 {
+	if !has_surplus.is_empty() {
 		// Determine if surplues can be deferred
 		if opts.defer_surpluses {
 			if can_defer_surpluses(state, opts, &total_surpluses) {
@@ -646,10 +657,10 @@ where
 		match opts.surplus_order {
 			SurplusOrder::BySize => {
 				// Compare b with a to sort high-low
-				has_surplus.sort_by(|a, b| b.1.votes.partial_cmp(&a.1.votes).unwrap());
+				has_surplus.sort_by(|a, b| b.1.votes.cmp(&a.1.votes));
 			}
 			SurplusOrder::ByOrder => {
-				has_surplus.sort_by(|a, b| a.1.order_elected.partial_cmp(&b.1.order_elected).unwrap());
+				has_surplus.sort_by(|a, b| a.1.order_elected.cmp(&b.1.order_elected));
 			}
 		}
 		
@@ -660,9 +671,9 @@ where
 		if has_surplus.len() > 1 && has_surplus[0].1.votes == has_surplus[1].1.votes {
 			let max_votes = &has_surplus[0].1.votes;
 			let has_surplus = has_surplus.into_iter().filter_map(|(c, cc)| if &cc.votes == max_votes { Some(c) } else { None }).collect();
-			elected_candidate = TieStrategy::Prompt.choose_highest(has_surplus)?;
+			elected_candidate = choose_highest(state, opts, has_surplus)?;
 		} else {
-			elected_candidate = has_surplus.first_mut().unwrap().0;
+			elected_candidate = has_surplus[0].0;
 		}
 		
 		distribute_surplus(state, &opts, elected_candidate);
@@ -905,20 +916,35 @@ where
 	state.loss_fraction.transfer(&-checksum);
 }
 
-fn bulk_elect<N: Number>(state: &mut CountState<N>) -> bool {
+fn bulk_elect<N: Number>(state: &mut CountState<N>, opts: &STVOptions) -> Result<bool, STVError> {
 	if state.election.candidates.len() - state.num_excluded <= state.election.seats {
 		state.kind = None;
 		state.title = "Bulk election".to_string();
 		
 		// Bulk elect all remaining candidates
-		let mut hopefuls: Vec<(&&Candidate, &mut CountCard<N>)> = state.candidates.iter_mut()
+		let mut hopefuls: Vec<&Candidate> = state.election.candidates.iter()
-			.filter(|(_, cc)| cc.state == CandidateState::Hopeful)
+			.filter(|c| state.candidates.get(c).unwrap().state == CandidateState::Hopeful)
 			.collect();
 		
-		// TODO: Handle ties
+		while !hopefuls.is_empty() {
-		hopefuls.sort_unstable_by(|a, b| a.1.votes.partial_cmp(&b.1.votes).unwrap());
+			let max_votes = hopefuls.iter()
-		
+				.max_by(|a, b| state.candidates.get(**a).unwrap().votes.cmp(&state.candidates.get(**b).unwrap().votes))
-		for (candidate, count_card) in hopefuls.into_iter() {
+				.unwrap();
+			let max_votes = &state.candidates.get(max_votes).unwrap().votes;
+			let max_hopefuls: Vec<&Candidate> = hopefuls.iter()
+				.filter(|c| &state.candidates.get(**c).unwrap().votes == max_votes)
+				.map(|c| *c)
+				.collect();
+			
+			let candidate;
+			if max_hopefuls.len() > 1 {
+				// Handle ties
+				candidate = choose_highest(state, opts, max_hopefuls)?;
+			} else {
+				candidate = max_hopefuls[0];
+			}
+			
+			let count_card = state.candidates.get_mut(candidate).unwrap();
 			count_card.state = CandidateState::Elected;
 			state.num_elected += 1;
 			count_card.order_elected = state.num_elected as isize;
@@ -928,11 +954,13 @@ fn bulk_elect<N: Number>(state: &mut CountState<N>) -> bool {
 				"{} are elected to fill the remaining vacancies.",
 				vec![&candidate.name]
 			);
+			
+			hopefuls.remove(hopefuls.iter().position(|c| *c == candidate).unwrap());
 		}
 		
-		return true;
+		return Ok(true);
 	}
-	return false;
+	return Ok(false);
 }
 
 fn hopefuls_to_bulk_exclude<'a, N: Number>(state: &CountState<'a, N>, _opts: &STVOptions) -> Vec<&'a Candidate> {
@@ -943,8 +971,8 @@ fn hopefuls_to_bulk_exclude<'a, N: Number>(state: &CountState<'a, N>, _opts: &ST
 		.collect();
 	
 	// Sort by votes
-	// TODO: Handle ties
+	// NB: Unnecessary to handle ties, as ties will be rejected at "Do not exclude if this could change the order of exclusion"
-	hopefuls.sort_unstable_by(|a, b| a.1.votes.partial_cmp(&b.1.votes).unwrap());
+	hopefuls.sort_unstable_by(|a, b| a.1.votes.cmp(&b.1.votes));
 	
 	let total_surpluses = state.candidates.iter()
 		.filter(|(_, cc)| &cc.votes > state.quota.as_ref().unwrap())
@@ -954,11 +982,6 @@ fn hopefuls_to_bulk_exclude<'a, N: Number>(state: &CountState<'a, N>, _opts: &ST
 	for i in 0..hopefuls.len() {
 		let try_exclude = &hopefuls[0..hopefuls.len()-i];
 		
-		// Do not exclude if this splits tied candidates
-		if i != 0 && try_exclude.last().unwrap().1.votes == hopefuls[hopefuls.len()-i].1.votes {
-			continue;
-		}
-		
 		// Do not exclude if this leaves insufficient candidates
 		if state.num_elected + hopefuls.len() - try_exclude.len() < state.election.seats {
 			continue;
@@ -966,7 +989,7 @@ fn hopefuls_to_bulk_exclude<'a, N: Number>(state: &CountState<'a, N>, _opts: &ST
 		
 		// Do not exclude if this could change the order of exclusion
 		let total_votes = try_exclude.into_iter().fold(N::new(), |agg, (_, cc)| agg + &cc.votes);
-		if i != 0 && total_votes + &total_surpluses > hopefuls[hopefuls.len()-i].1.votes {
+		if i != 0 && total_votes + &total_surpluses >= hopefuls[hopefuls.len()-i].1.votes {
 			continue;
 		}
 		
@@ -991,22 +1014,22 @@ where
 	}
 	
 	// Exclude lowest ranked candidate
-	if excluded_candidates.len() == 0 {
+	if excluded_candidates.is_empty() {
 		let mut hopefuls: Vec<(&Candidate, &CountCard<N>)> = state.election.candidates.iter() // Present in order in case of tie
 			.map(|c| (c, state.candidates.get(c).unwrap()))
 			.filter(|(_, cc)| cc.state == CandidateState::Hopeful)
 			.collect();
 		
 		// Sort by votes
-		hopefuls.sort_by(|a, b| a.1.votes.partial_cmp(&b.1.votes).unwrap());
+		hopefuls.sort_by(|a, b| a.1.votes.cmp(&b.1.votes));
 		
 		// Handle ties
 		if hopefuls.len() > 1 && hopefuls[0].1.votes == hopefuls[1].1.votes {
 			let min_votes = &hopefuls[0].1.votes;
 			let hopefuls = hopefuls.into_iter().filter_map(|(c, cc)| if &cc.votes == min_votes { Some(c) } else { None }).collect();
-			excluded_candidates = vec![TieStrategy::Prompt.choose_lowest(hopefuls)?];
+			excluded_candidates = vec![choose_lowest(state, opts, hopefuls)?];
 		} else {
-			excluded_candidates = vec![&hopefuls.first().unwrap().0];
+			excluded_candidates = vec![&hopefuls[0].0];
 		}
 	}
 	
@@ -1031,14 +1054,13 @@ where
 {
 	// Cannot filter by raw vote count, as candidates may have 0.00 votes but still have recorded ballot papers
 	let mut excluded_with_votes: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter()
-		//.filter(|(_, cc)| cc.state == CandidateState::EXCLUDED && !cc.votes.is_zero())
+		.filter(|(_, cc)| cc.state == CandidateState::Excluded && cc.parcels.iter().any(|p| !p.is_empty()))
-		.filter(|(_, cc)| cc.state == CandidateState::Excluded && cc.parcels.iter().any(|p| p.len() > 0))
 		.collect();
 	
-	if excluded_with_votes.len() > 0 {
+	if !excluded_with_votes.is_empty() {
-		excluded_with_votes.sort_unstable_by(|a, b| a.1.order_elected.partial_cmp(&b.1.order_elected).unwrap());
+		excluded_with_votes.sort_unstable_by(|a, b| a.1.order_elected.cmp(&b.1.order_elected));
 		
-		let order_excluded = excluded_with_votes.first().unwrap().1.order_elected;
+		let order_excluded = excluded_with_votes[0].1.order_elected;
 		let excluded_candidates: Vec<&Candidate> = excluded_with_votes.into_iter()
 			.filter(|(_, cc)| cc.order_elected == order_excluded)
 			.map(|(c, _)| *c)
@@ -1127,7 +1149,7 @@ where
 					}
 				}
 				
-				if remaining_votes.len() > 0 {
+				if !remaining_votes.is_empty() {
 					votes_remain = true;
 				}
 				
@@ -1145,9 +1167,9 @@ where
 				panic!("--exclusion parcels_by_order is incompatible with --bulk-exclude");
 			}
 			
-			let count_card = state.candidates.get_mut(excluded_candidates.first().unwrap()).unwrap();
+			let count_card = state.candidates.get_mut(excluded_candidates[0]).unwrap();
 			votes = count_card.parcels.remove(0);
-			votes_remain = count_card.parcels.len() > 0;
+			votes_remain = !count_card.parcels.is_empty();
 			
 			// Update votes
 			let votes_transferred = votes.iter().fold(N::new(), |acc, v| acc + &v.value);
@@ -1156,7 +1178,7 @@ where
 		}
 	}
 	
-	if votes.len() > 0 {
+	if !votes.is_empty() {
 		let value = &votes[0].value / &votes[0].ballot.orig_value;
 		
 		// Count next preferences
@@ -1220,3 +1242,155 @@ fn finished_before_stage<N: Number>(state: &CountState<N>) -> bool {
 	}
 	return false;
 }
+
+fn choose_highest<'c, N: Number>(state: &CountState<N>, opts: &STVOptions, candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
+	for strategy in opts.ties.iter() {
+		match strategy.choose_highest(state, &candidates) {
+			Ok(c) => {
+				return Ok(c);
+			}
+			Err(e) => {
+				if let STVError::UnresolvedTie = e {
+					continue;
+				} else {
+					return Err(e);
+				}
+			}
+		}
+	}
+	panic!("Unable to resolve tie");
+}
+
+fn choose_lowest<'c, N: Number>(state: &CountState<N>, opts: &STVOptions, candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
+	for strategy in opts.ties.iter() {
+		match strategy.choose_lowest(state, &candidates) {
+			Ok(c) => {
+				return Ok(c);
+			}
+			Err(e) => {
+				if let STVError::UnresolvedTie = e {
+					continue;
+				} else {
+					return Err(e);
+				}
+			}
+		}
+	}
+	return Err(STVError::UnresolvedTie);
+}
+
+fn init_tiebreaks<N: Number>(state: &mut CountState<N>, opts: &STVOptions) {
+	if !opts.ties.iter().any(|t| t == &TieStrategy::Forwards) && !opts.ties.iter().any(|t| t == &TieStrategy::Backwards) {
+		return;
+	}
+	
+	// Sort candidates in this stage by votes, grouping by ties
+	let mut sorted_candidates: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter().collect();
+	sorted_candidates.sort_unstable_by(|a, b| a.1.votes.cmp(&b.1.votes));
+	let sorted_candidates: Vec<Vec<(&&Candidate, &CountCard<N>)>> = sorted_candidates.into_iter()
+		.group_by(|(_, cc)| &cc.votes)
+		.into_iter()
+		.map(|(_, candidates)| candidates.collect())
+		.collect();
+	
+	// Update forwards tie-breaking order
+	if opts.ties.iter().any(|t| t == &TieStrategy::Forwards) {
+		let mut hm: HashMap<&Candidate, usize> = HashMap::new();
+		for (i, group) in sorted_candidates.iter().enumerate() {
+			for (candidate, _) in group.iter() {
+				hm.insert(candidate, i);
+			}
+		}
+		state.forwards_tiebreak = Some(hm);
+	}
+	
+	// Update backwards tie-breaking order
+	if opts.ties.iter().any(|t| t == &TieStrategy::Backwards) {
+		let mut hm: HashMap<&Candidate, usize> = HashMap::new();
+		for (i, group) in sorted_candidates.iter().enumerate() {
+			for (candidate, _) in group.iter() {
+				hm.insert(candidate, i);
+			}
+		}
+		state.backwards_tiebreak = Some(hm);
+	}
+}
+
+fn update_tiebreaks<N: Number>(state: &mut CountState<N>, _opts: &STVOptions) {
+	if let None = state.forwards_tiebreak {
+		if let None = state.backwards_tiebreak {
+			return;
+		}
+	}
+	
+	// Sort candidates in this stage by votes, grouping by ties
+	let mut sorted_candidates: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter().collect();
+	sorted_candidates.sort_unstable_by(|a, b| a.1.votes.cmp(&b.1.votes));
+	let sorted_candidates: Vec<Vec<&Candidate>> = sorted_candidates.into_iter()
+		.group_by(|(_, cc)| &cc.votes)
+		.into_iter()
+		.map(|(_, candidates)| candidates.map(|(c, _)| *c).collect())
+		.collect();
+	
+	// Update forwards tie-breaking order
+	if let Some(hm) = state.forwards_tiebreak.as_mut() {
+		// TODO: Check if already completely sorted
+		let mut sorted_last_round: Vec<(&&Candidate, &usize)> = hm.iter().collect();
+		sorted_last_round.sort_unstable_by(|a, b| a.1.cmp(b.1));
+		let sorted_last_round: Vec<Vec<&Candidate>> = sorted_last_round.into_iter()
+			.group_by(|(_, v)| **v)
+			.into_iter()
+			.map(|(_, group)| group.map(|(c, _)| *c).collect())
+			.collect();
+		
+		let mut i: usize = 0;
+		for mut group in sorted_last_round.into_iter() {
+			if group.len() == 1 {
+				hm.insert(group[0], i);
+				i += 1;
+				continue;
+			} else {
+				// Tied in last round - refer to this round
+				group.sort_unstable_by(|a, b|
+					sorted_candidates.iter().position(|x| x.contains(a)).unwrap()
+					.cmp(&sorted_candidates.iter().position(|x| x.contains(b)).unwrap())
+				);
+				let tied_last_round = group.into_iter()
+					.group_by(|c| sorted_candidates.iter().position(|x| x.contains(c)).unwrap());
+				
+				for (_, group2) in tied_last_round.into_iter() {
+					for candidate in group2 {
+						hm.insert(candidate, i);
+					}
+					i += 1;
+				}
+			}
+		}
+	}
+	
+	// Update backwards tie-breaking order
+	if let Some(hm) = state.backwards_tiebreak.as_mut() {
+		let hm_orig = hm.clone();
+		let mut i: usize = 0;
+		for group in sorted_candidates.iter() {
+			if group.len() == 1 {
+				hm.insert(group[0], i);
+				i += 1;
+				continue;
+			} else {
+				// Tied in this round - refer to last round
+				let mut tied_this_round: Vec<&Candidate> = group.into_iter().map(|c| *c).collect();
+				tied_this_round.sort_unstable_by(|a, b| hm_orig.get(a).unwrap().cmp(hm_orig.get(b).unwrap()));
+				let tied_this_round = tied_this_round.into_iter()
+					.group_by(|c| hm_orig.get(c).unwrap());
+				
+				for (_, group2) in tied_this_round.into_iter() {
+					for candidate in group2 {
+						hm.insert(candidate, i);
+					}
+					i += 1;
+				}
+			}
+		}
+	}
+}

src/stv/wasm.rs

@@ -55,16 +55,17 @@ macro_rules! impl_type {
 		
 		#[wasm_bindgen]
 		#[allow(non_snake_case)]
-		pub fn [<count_init_$type>](state: &mut [<CountState$type>], opts: &stv::STVOptions) {
+		pub fn [<count_init_$type>](state: &mut [<CountState$type>], opts: &STVOptionsWrapper) {
-			stv::count_init(&mut state.0, &opts);
+			stv::count_init(&mut state.0, &opts.0);
 		}
 		
 		#[wasm_bindgen]
 		#[allow(non_snake_case)]
-		pub fn [<count_one_stage_$type>](state: &mut [<CountState$type>], opts: &stv::STVOptions) -> Result<bool, JsValue> {
+		pub fn [<count_one_stage_$type>](state: &mut [<CountState$type>], opts: &STVOptionsWrapper) -> Result<bool, JsValue> {
-			match stv::count_one_stage(&mut state.0, &opts) {
+			match stv::count_one_stage(&mut state.0, &opts.0) {
 				Ok(v) => Ok(v),
 				Err(stv::STVError::RequireInput) => Err("RequireInput".into()),
+				Err(stv::STVError::UnresolvedTie) => Err("UnresolvedTie".into()),
 			}
 		}
 		
@@ -72,20 +73,20 @@ macro_rules! impl_type {
 		
 		#[wasm_bindgen]
 		#[allow(non_snake_case)]
-		pub fn [<init_results_table_$type>](election: &[<Election$type>], opts: &stv::STVOptions) -> String {
+		pub fn [<init_results_table_$type>](election: &[<Election$type>], opts: &STVOptionsWrapper) -> String {
-			return init_results_table(&election.0, opts);
+			return init_results_table(&election.0, &opts.0);
 		}
 		
 		#[wasm_bindgen]
 		#[allow(non_snake_case)]
-		pub fn [<describe_count_$type>](filename: String, election: &[<Election$type>], opts: &stv::STVOptions) -> String {
+		pub fn [<describe_count_$type>](filename: String, election: &[<Election$type>], opts: &STVOptionsWrapper) -> String {
-			return describe_count(filename, &election.0, opts);
+			return describe_count(filename, &election.0, &opts.0);
 		}
 		
 		#[wasm_bindgen]
 		#[allow(non_snake_case)]
-		pub fn [<update_results_table_$type>](stage_num: usize, state: &[<CountState$type>], opts: &stv::STVOptions) -> Array {
+		pub fn [<update_results_table_$type>](stage_num: usize, state: &[<CountState$type>], opts: &STVOptionsWrapper) -> Array {
-			return update_results_table(stage_num, &state.0, opts);
+			return update_results_table(stage_num, &state.0, &opts.0);
 		}
 		
 		#[wasm_bindgen]
@@ -139,6 +140,9 @@ impl_type!(Fixed);
 impl_type!(NativeFloat64);
 impl_type!(Rational);
 
+#[wasm_bindgen]
+pub struct STVOptionsWrapper(stv::STVOptions<'static>);
+
 // Reporting
 
 fn init_results_table<N: Number>(election: &Election<N>, opts: &stv::STVOptions) -> String {

src/ties.rs

@@ -15,7 +15,8 @@
  *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
-use crate::election::Candidate;
+use crate::election::{Candidate, CountState};
+use crate::numbers::Number;
 use crate::stv::STVError;
 
 #[allow(unused_imports)]
@@ -24,6 +25,7 @@ use wasm_bindgen::prelude::wasm_bindgen;
 #[allow(unused_imports)]
 use std::io::{stdin, stdout, Write};
 
+#[derive(PartialEq)]
 pub enum TieStrategy<'s> {
 	Forwards,
 	Backwards,
@@ -32,10 +34,42 @@ pub enum TieStrategy<'s> {
 }
 
 impl<'s> TieStrategy<'s> {
-	pub fn choose_highest<'c>(&self, candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
+	pub fn describe(&self) -> String {
 		match self {
-			Self::Forwards => { todo!() }
+			Self::Forwards => "forwards",
-			Self::Backwards => { todo!() }
+			Self::Backwards => "backwards",
+			Self::Random(_) => todo!(),
+			Self::Prompt => "prompt",
+		}.to_string()
+	}
+	
+	pub fn choose_highest<'c, N: Number>(&self, state: &CountState<N>, candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
+		match self {
+			Self::Forwards => {
+				let mut candidates = candidates.clone();
+				candidates.sort_unstable_by(|a, b|
+					// Compare b to a to sort high-to-low
+					state.forwards_tiebreak.as_ref().unwrap().get(b).unwrap()
+						.cmp(&state.forwards_tiebreak.as_ref().unwrap().get(a).unwrap())
+					);
+				if state.forwards_tiebreak.as_ref().unwrap().get(candidates[0]).unwrap() == state.forwards_tiebreak.as_ref().unwrap().get(candidates[1]).unwrap() {
+					return Err(STVError::UnresolvedTie);
+				} else {
+					return Ok(candidates[0]);
+				}
+			}
+			Self::Backwards => {
+				let mut candidates = candidates.clone();
+				candidates.sort_unstable_by(|a, b|
+					state.backwards_tiebreak.as_ref().unwrap().get(b).unwrap()
+						.cmp(&state.backwards_tiebreak.as_ref().unwrap().get(a).unwrap())
+					);
+				if state.backwards_tiebreak.as_ref().unwrap().get(candidates[0]).unwrap() == state.backwards_tiebreak.as_ref().unwrap().get(candidates[1]).unwrap() {
+					return Err(STVError::UnresolvedTie);
+				} else {
+					return Ok(candidates[0]);
+				}
+			}
 			Self::Random(_seed) => { todo!() }
 			Self::Prompt => {
 				return prompt(candidates);
@@ -43,22 +77,44 @@ impl<'s> TieStrategy<'s> {
 		}
 	}
 	
-	pub fn choose_lowest<'c>(&self, candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
+	pub fn choose_lowest<'c, N: Number>(&self, state: &CountState<N>, candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
 		match self {
-			Self::Forwards => { todo!() }
+			Self::Forwards => {
-			Self::Backwards => { todo!() }
+				let mut candidates = candidates.clone();
+				candidates.sort_unstable_by(|a, b|
+					state.forwards_tiebreak.as_ref().unwrap().get(a).unwrap()
+						.cmp(&state.forwards_tiebreak.as_ref().unwrap().get(b).unwrap())
+					);
+				if state.forwards_tiebreak.as_ref().unwrap().get(candidates[0]).unwrap() == state.forwards_tiebreak.as_ref().unwrap().get(candidates[1]).unwrap() {
+					return Err(STVError::UnresolvedTie);
+				} else {
+					return Ok(candidates[0]);
+				}
+			}
+			Self::Backwards => {
+				let mut candidates = candidates.clone();
+				candidates.sort_unstable_by(|a, b|
+					state.backwards_tiebreak.as_ref().unwrap().get(a).unwrap()
+						.cmp(&state.backwards_tiebreak.as_ref().unwrap().get(b).unwrap())
+					);
+				if state.backwards_tiebreak.as_ref().unwrap().get(candidates[0]).unwrap() == state.backwards_tiebreak.as_ref().unwrap().get(candidates[1]).unwrap() {
+					return Err(STVError::UnresolvedTie);
+				} else {
+					return Ok(candidates[0]);
+				}
+			}
 			Self::Random(_seed) => {
-				return self.choose_highest(candidates);
+				return self.choose_highest(state, candidates);
 			}
 			Self::Prompt => {
-				return self.choose_highest(candidates);
+				return self.choose_highest(state, candidates);
 			}
 		}
 	}
 }
 
 #[cfg(not(target_arch = "wasm32"))]
-fn prompt<'c>(candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
+fn prompt<'c>(candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
 	println!("Multiple tied candidates:");
 	for (i, candidate) in candidates.iter().enumerate() {
 		println!("{}. {}", i + 1, candidate.name);
@@ -93,7 +149,7 @@ extern "C" {
 }
 
 #[cfg(target_arch = "wasm32")]
-fn prompt<'c>(candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
+fn prompt<'c>(candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
 	let mut message = String::from("Multiple tied candidates:\n");
 	for (i, candidate) in candidates.iter().enumerate() {
 		message.push_str(&format!("{}. {}\n", i + 1, candidate.name));

tests/aec.rs

@@ -64,6 +64,7 @@ fn aec_tas19_rational() {
 		quota: stv::QuotaType::Droop,
 		quota_criterion: stv::QuotaCriterion::GreaterOrEqual,
 		quota_mode: stv::QuotaMode::Static,
+		ties: vec![],
 		surplus: stv::SurplusMethod::UIG,
 		surplus_order: stv::SurplusOrder::ByOrder,
 		transferable_only: false,

tests/ers97.rs

@@ -38,6 +38,7 @@ fn ers97_rational() {
 		quota: stv::QuotaType::DroopExact,
 		quota_criterion: stv::QuotaCriterion::GreaterOrEqual,
 		quota_mode: stv::QuotaMode::ERS97,
+		ties: vec![],
 		surplus: stv::SurplusMethod::EG,
 		surplus_order: stv::SurplusOrder::BySize,
 		transferable_only: true,

tests/prsa.rs

@@ -32,6 +32,7 @@ fn prsa1_rational() {
 		quota: stv::QuotaType::Droop,
 		quota_criterion: stv::QuotaCriterion::GreaterOrEqual,
 		quota_mode: stv::QuotaMode::Static,
+		ties: vec![],
 		surplus: stv::SurplusMethod::EG,
 		surplus_order: stv::SurplusOrder::ByOrder,
 		transferable_only: true,

tests/scotland.rs

@@ -39,6 +39,7 @@ fn scotland_linn07_fixed5() {
 		quota: stv::QuotaType::Droop,
 		quota_criterion: stv::QuotaCriterion::GreaterOrEqual,
 		quota_mode: stv::QuotaMode::Static,
+		ties: vec![],
 		surplus: stv::SurplusMethod::WIG,
 		surplus_order: stv::SurplusOrder::BySize,
 		transferable_only: false,