predict.rating {PlayerRatings}

Predict Result Of Games Based On Player Ratings

Description

Predict the result of two-player or multi-player games, given the estimated ratings for each player.

Usage

## S3 method for class 'rating'
predict(object, newdata, tng=15, trat=NULL, gamma=30, 
  thresh, placing = FALSE, ...)

Arguments

object

An object of class "rating".

newdata

For two player games, a dataframe containing three variables: (1) a numeric vector denoting the time period in which the game is taking place (2) a numeric or character identifier for player one (3) a numeric or character identifier for player two. The time period can contain missing values as it is not used for the prediction. For N-player games (i.e. for objects created by the elom function), the player identifiers should be in columns 2 to N-1. This argument cannot be missing; if predictions on the original dataset are required, then this dataset must be passed to the prediction function.

tng

A single value. If the number of games played by any player is below this value, then either the prediction will be a missing value, or the prediction will be based on trat.

trat

A single number (for Elo and EloM), or a vector of length two (for Glicko or Glicko-2 or Stephenson) giving the rating and deviation parameters to be used for players who have played less than tng games. If NULL then these predictions will be missing. The volatility parameter in Glicko-2 is not needed for predictions.

gamma

A player one advantage parameter; either a single value or a numeric vector equal to the number of rows in newdata. Positive values favour player one, while negative values favour player two. This could represent the advantage of playing at home, or the advantage of playing white for chess. The default value is roughly optimal for chess ratings. Ignored for multi-player.

thresh

A single value. If given, a binary vector is returned indicating whether the prediction is greater than this value. Ignored for multi-player.

placing

For multi-player only. If TRUE, predicted placings are given rather than expected base scores.

...

Not used.

Details

The function predicts the expectation of the game result. In two-player games, if the value of one is a win for player one, and the value of zero is a win for player two, and there are no other possibilities, then the prediction is the probability of a win for player one. This is not the case when draws are a possibility.

For multi-player predictions using objects produced by elom, expected base scores are given for each player. These are simply the difference between the rating of a player and the average of all players in the game, divided by 40.

Value

A numeric vector of predictions of two-player games, or a matrix of expected base scores for multi-player games, either of which may contain missing values.

See Also

elo, elom, metrics

Examples

afl <- aflodds[,c(2,3,4,7)]
train <- afl[afl$Week <= 80,]
test <- afl[afl$Week > 80,]
robj <- elo(train)
pvals <- predict(robj, test)

train <- riichi[riichi$Time <= 250,]
test <- riichi[riichi$Time > 250,]
robj <- elom(train)
predict(robj, test, trat = 1400, placing = TRUE)