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Round Robin Pairing (Shapes)

Overview​

A round robin is a pairing shape — every entrant meets every other entrant — and that shape can be applied by round generation as well as by a draw structure. The two are different tools:

ROUND_ROBIN draw typepairingProfile on an AD_HOC draw
Producesgroups, each a container structure with positioned entrantsrounds of matchUps, no groups
Groupssplits the draw into groups of structureOptions.groupSizenone — one schedule over all entrants
Repeat meetingsone meeting per pairencounters: 2, 3, …
Partial scheduleno — the full pairing set is materializedyes — roundsCount truncates
Finishing positionsderived from group talliesnone — rounds are independent

Use the draw type when the competition is organized into groups that produce finishing positions. Use a pairing shape when the competition is a league: one division, everyone plays everyone, possibly twice, possibly only partway through the season.

Applying a shape​

const { drawDefinition } = engine.generateDrawDefinition({
  drawType: 'AD_HOC',
  drawSize: 8,
  eventId,
  pairingProfile: {
    shape: 'ROUND_ROBIN',
    encounters: 2, // double round robin
    mirrored: true, // default — alternating encounters swap side order
  },
});
FieldTypeDefaultDescription
shapestring—ROUND_ROBIN is the shape currently supported
encountersnumber1How many times each pair meets. 2 is a double round robin, 3 a triple
mirroredbooleantrueSwap side order on alternating encounters, making a double round robin home-and-home

A roundsCount supplied alongside a pairingProfile truncates the schedule to a partial round robin (see below) rather than setting the number of rounds outright.

The schedule​

The shape produces entrants - 1 rounds per encounter, each round containing floor(entrants / 2) matchUps. Over a single encounter every pair meets exactly once — C(n, 2) matchUps in total.

With an odd number of entrants, one participant sits out each round: the circle method pairs against a bye position, and the resulting pairing is omitted. Eight entrants give 7 rounds of 4; five entrants give 5 rounds of 2.

The schedule comes from the same circle method the ROUND_ROBIN draw type uses to order group matchUps, so both paths agree on which meetings belong to which round.

Encounters and mirroring​

encounters: 2 replays the whole schedule a second time. With mirrored: true (the default) the second cycle swaps side order, so a pair that met with [A, B] in round 1 meets as [B, A] in round entrants. That side order is what carries home-and-away meaning for league scheduling; set mirrored: false to keep side order stable across encounters.

Partial round robins​

Not every league division completes its schedule — entrants withdraw, or a flight is too large for the season. Supplying roundsCount alongside a pairingProfile materializes only the first N rounds:

engine.generateDrawDefinition({
  drawType: 'AD_HOC',
  drawSize: 12,
  eventId,
  pairingProfile: { shape: 'ROUND_ROBIN' },
  roundsCount: 4, // the first 4 rounds of an 11-round schedule
});

Because only the meetings that occur are generated, an unplayed matchUp in a partial schedule is distinguishable from a meeting that was never scheduled at all.

Unsatisfiable requests are reported​

A request the shape cannot satisfy returns INVALID_VALUES rather than being quietly reduced to whatever happened to be possible:

  • a roundsCount greater than (entrants - 1) × encounters
  • an encounters value that is not a positive integer
  • an unrecognized shape
  • fewer than two entrants

Relationship to DrawMatic and Swiss​

All three pair participants into ad-hoc rounds, and they answer different questions:

  • DrawMatic pairs by rating, avoiding repeat opponents probabilistically. It does not guarantee that every entrant meets every other — with enableDoubleRobin it will schedule up to (entrants - 1) × 2 rounds, but the pairings are rating-weighted, not a replayed schedule.
  • Swiss pairs each round from the current standings, so the schedule cannot be known in advance.
  • A round robin shape is fully determined before play begins, which is what a published league fixture list requires.