TieBreaker

Overview

TieBreaker deals within groups ties in tournaments that has group-like equivalents. Such tournaments include:

• GroupStage
• FFA (when using a multiple match final round)

But TieBreaker will break ties for any tournament that implements rawPositions, a special method that converts results into a raw array of positions per "group".

Usage

Unlike every other tournament type, this tournament CAN NOT be created directly. It needs a finished tournament instance to be created from, and the number of players we want to pick from this tournament:

var gs = new GroupStage(8, { groupSize: 4 });
// score groupstage so that we have some ties
gs.matches.forEach(function (m, i) {
  if (m.id.s === 1) {
    gs.score(m.id, i === 2 ? [1,0] : [1, 1]);
  }
  if (m.id.s === 2) {
    gs.score(m.id, ([4].indexOf(m.id.r) >= 0) ? [1, 0] : [0, 1]);
  }
});
gs.isDone(); // true

In this case the group stage is tied in the following ways:

• group one: 1st: [1], 2nd: [3,8], 4th: [6]
• group two: 1st: [4,5,7], 4th: [2]

Then, we may create tiebreakers in one of two ways, the simplest creates an FFA style match for each group where we need to break it up:

var tb = TieBreaker.from(gs, 4); // want the top 4
tb.matches;
[ { id: { s: 1, r: 1, m: 1 }, // group 1 tiebreaker
    p: [ 3, 8 ] },
  { id: { s: 2, r: 1, m: 1 }, // group 2 tiebreaker
    p: [ 4, 5, 7 ] } ]

tb.score(tb.matches[0].id, [2,1]);
tb.score(tb.matches[1].id, [3,2,1]);
var top4 = tb.results().slice(0, 4); // will contain results for 1,3,4,5

The more advanced creates mini groupstages for each group involving the tied players:

var tb = TieBreaker.from(gs, 4, { grouped: true });
tb.matches;
[ { id: { s: 1, r: 1, m: 1 }, p: [ 3, 8 ] },
  // group 2 tiebreaker subgroup
  { id: { s: 2, r: 1, m: 1 }, p: [ 5, 7 ] },
  { id: { s: 2, r: 2, m: 1 }, p: [ 4, 7 ] },
  { id: { s: 2, r: 3, m: 1 }, p: [ 4, 5 ] } ]

Because tb.matches is a non-empty array, there were ties that meant isolating the top 4 was impossible. Depending on how many players we request to forward (in this case 4), TieBreaker may need more or fewer matches played.

Resolution

At the end of the TieBreaker tournament, you can call results and get the newly positioned results array. However, unless you were creating the tournament in strict mode, the ties may not have been broken fully.

tb.matches.forEach(function (m) {
// tie all the tiebreaker matches in group 2 (continuing grouped example)
  tb.score(m.id, (m.id.s === 2) ? [1,1] : [2,1]);
});
tb.isDone(); // true
TieBreaker.isNecessary(tb, 4); // true

In this case we would need to recreate the TieBreaker from the previous instance. Until the conflict has been resolved, you will need to keep doing this:

// recreate tiebreaker from partially broken/unbroken tiebreaker instance
var tb2 = TieBreaker.from(tb, 4);
tb2.matches;
[ { id: { s: 2, r: 1, m: 1 }, p: [ 5, 7 ] },
  { id: { s: 2, r: 2, m: 1 }, p: [ 4, 7 ] },
  { id: { s: 2, r: 3, m: 1 }, p: [ 4, 5 ] } ]

Repeating this procedure will eventually lead to a tiebreaker result where !TieBreaker.isNecessary(prevTb, 4). In this case you can pick out the top 4 by slicing the results, or simply using .from on your next tournament.

tb2.isDone(); // true
TieBreaker.isNecessary(tb2, 4); // false - assume we unbroke group 2 in tb2
var top4 = tb2.results().slice(0, 4); // results for top 4

// send the top 4 players from the groupstage to a two-round duel tournament
var duel = Duel.from(tb2, 4);

Why should you use this module

Without going into detail, it is fairly easy to end up in a situation where you have many different multi-way ties. The following is a GroupStage test case:

• group one: 1sts: [1,2,6], 4ths: [8]
• group two: 1sts: [5], 2nds: [3,4,7]

If we get the results from GroupStage, it will say that [1,2,5,6] are all 1st placers, and thus tie all these four results[i].pos attributes at 1. If we wanted the top 4 to proceed to a different tournament we would end up picking three players from group 1 and one player from group 2.

While this seems terrible, GroupStage have nonetheless computed the results to the best of its knowledge.

By specifying the number of players you want to extract, TieBreaker can create matches needed to forward the top n players (a multiple of the number of groups) to another tournament fairly.

Example

Using the ties outlined above, if we:

Require top 4

Then need to break:

• 1st place cluster [1,2,6] - then pick top 2 to proceed
• 2nd place cluster [3,4,7] - then pick winner to proceed

That gives 3 out of the 4 to proceed, and the last is player 5 who won his group alone and is guaranteed through.

Require top 2

Then only need to break the 1st place cluster in group 1, because we know 5 is one of the top 2.

Require top 6

Only need to break the 2nd place cluster from group 2, because we know [1,2,6] are all in the top 6.

Viewing results

Results out from a TieBreaker instance are identical to the results received from the tournament we are breaking. The only difference is that we modify the pos attributes in two ways:

• Until the TieBreaker is done - we demote players in the TieBreaker to an assumed worst outcome
• After TieBreaker is done - we can safely pick the top n (fairly) by simply filtering by r.pos <= n, or by calling slice(0, n)
• The gpos attributes are modified
• The pos attributes are at the end built up like GroupStage

Limitations

TieBreaker only allows a multiple of the number of groups/sections to be chosen, lest unfair inferences about positions between groups needs to be made. See issue #3.

Extras

While TieBreaker implements results and from slightly differently than any other tournament, is still a perfectly valid tournament. All the methods available on the tournament base class exist on TieBreaker. Read the tournament API

License

MIT-Licensed. See LICENSE file for details.