timotree3 / rcir

Ranked Choice Instant Runoff library written in Rust

RCIR

RCIR is a ranked choice instant runoff library written in rust. It's a work in progress. The library is in the rcir directory, and a sample binary is in the rcir_csv directory.

In the result of a tie for last place and no winner, all the last place candidates are removed, so it is not a 'Spoiler Proof' method Spoiler Effect + Resistance to tactical voting

RCIR will not mutate the input and aims to have as few restrictions on data types as possible

Example

Voter A	Voter B	Voter C	Voter D	Voter E
Bob	Sue	Bill	Bob	Sue
Bill	Bob	Sue	Bill	Bob
Sue	Bill	Bob	Sue	Bill

This would result in an ElectionResult::Winner(&"sue") under either operational mode

Tie Example

Voter A	Voter B
Bob	Sue

This would result in an ElectionResult::Tie([&"Bob", &"Sue"]) under either operational mode

Modes of operation

RCIR has 2 modes of operation:

• Complete Majority
• Remaining Majority

The differences between the two can best be explained with this sample:

Start

Voter A	Voter B	Voter C	Voter D	Voter E
Alice	Bob	Chris	Sam	Alice
Sam	Sam	Bob	Chris	Chris

After Round 1

Bob, Chris, and Sam are eliminated (lowest vote getters)

Voter A	Voter B	Voter C	Voter D	Voter E
Alice	_	_	_	Alice
_	_	_	_	_

Under CompleteMajority, there is no winner and the result would be: ElectionError::NoMajorityWinner because Alice has 2/5 votes, which is below the 50% threshold for a complete majority.

Under RemainingMajority, the result would be an ElectionResult::Winner(&"Alice") because Alice has 100% (2/2) of the remaining ballots of voters who still have candidates left.