Elo rating in Go

This library implements an Elo rating system in Golang.

Usage

The Elo system includes three factors that can be modified: kfactor, d and s.

The d value is always a constant and the kfactor and s values can be calculated via different implementations. This library includes some common implementations for both, but the user may code their own.

Example usage with default values:

// This initializes an elo object with:
// constant k-factor of 32
// d = 400
// linear implementation of s (1 for win, 0 for loss, 1/n for draw)
e := elo.NewEloDefault()

// Get the probability of a player with a rating of 1750 to beat 
// a player with a rating of 1500 with 2 decimals of precission.
expScore := e.GetExpectedScore(1750, 1500, 2)

// Get the new ratings when a player of rating of 1750 beats
// a player with a rating of 1500.
// Use 0 to indicate the first player wins, 1 for the second player
// and 2 for a draw.
ratings := []int{1750, 1500}
newRatiings, err := e.GetNewRatings(ratings, 0)


teamA := []int{1000, 1500}
teamB := []int{1300, 1400}
ratings := [][]int{teamA, teamB}

// Get the new ratings when teamB beats teamA in a 2vs2 match.
newRatings, err := e.GetNewRatingsTeams(ratings, 1)


// Get the new ratings when there is a draw in a 1vs1vs1 match.
ratings := []int{1000, 1200, 1500}
newRatiings, err := e.GetNewRatings(ratings, 3)

Example initializacion with custom values:

// kCalculatorCustom is an object that implements a custom k function
type kCalculatorCustom struct {
    minValue float64
    maxValue float64
    threshhold int
}

func newKCalculatorCustom(minValue, maxValue float64, threshhold int) *kCalculatorCustom {
    return &kCalculatorCustom {
        minValue: minValue,
        maxValue: maxValue,
        threshhold: threshhold,
    }
}

func (c *kCalculatorCustom) getKFactor(rating int) float64 {
    if rating < c.threshhold {
        return c.minValue
    }
    
    return c.maxValue
}

e := nelo.NewElo(200, elo.NewSCalculatorLinear(), newKCalculatorCustom(20, 40, 1500))