computeRanking.R

computeRkWR <- function(scoreA, scoreB, rankingA, rankingB, weight) {
  if (abs(rankingA - rankingB) < 10) {
    swap <- (as.numeric(scoreB > scoreA) 
             - as.numeric(scoreA > scoreB) 
             + (rankingA - rankingB)*0.1)
  } else {
    swap <- 2*(as.numeric(scoreB > scoreA)*as.numeric(rankingA > rankingB) 
               - as.numeric(scoreA > scoreB)*as.numeric(rankingB > rankingA))
    + as.numeric(scoreA == scoreB)*sign(rankingA - rankingB)
  }
  
  if (abs(scoreA - scoreB > 15))
    weight <- weight*1.5
  rankingA <- rankingA - swap*weight
  rankingB <- rankingB + swap*weight
  return(list(rankingA = rankingA, rankingB = rankingB))
}

computeRkWR_alt <- function(scoreA, scoreB, rankingA, rankingB, weight) {
  swap <- (as.numeric(scoreB > scoreA) 
           - as.numeric(scoreA > scoreB) 
           + (rankingA - rankingB)*0.1)
  
  if (abs(scoreA - scoreB > 15))
    weight <- weight*1.5
  rankingA <- rankingA - swap*weight
  rankingB <- rankingB + swap*weight
  return(list(rankingA = rankingA, rankingB = rankingB))
}

computeRkELO <- function(scoreA, scoreB, rankingA, rankingB, K) {
  D <- rankingA - rankingB
  pDA <- 1/(1+10**(-D/20))
  outcome <- as.numeric(scoreA > scoreB) + 0.5*as.numeric(scoreA == scoreB)
  swap <- K*(outcome - pDA)
  rankingA <- rankingA + swap
  rankingB <- rankingB - swap
  return(list(rankingA = rankingA, rankingB = rankingB))
}

computeRkELOd <- function(scoreA, scoreB, rankingA, rankingB, K) {
  D <- rankingA - rankingB
  pDA <- 1/(1+10**(-D/20))
  outcome <- ifelse(scoreA == 0 & scoreB == 0, 0.5, scoreA/(scoreA + scoreB))
  swap <- K*(outcome - pDA)
  rankingA <- rankingA + swap
  rankingB <- rankingB - swap
  return(list(rankingA = rankingA, rankingB = rankingB))
}

computeRanking <- function(match, type = c("WR","ELO","WRa","ELOd"), bonusReceiver = TRUE) {
  teamA <- match@teamA
  teamB <- match@teamB
  if (type == "WR")
    newRanking <- computeRkWR(match@scoreA, match@scoreB, teamA@ranking + as.numeric(bonusReceiver)*3, 
                              teamB@ranking, match@weight) else if (type == "ELO")
                                newRanking <- computeRkELO(match@scoreA, match@scoreB, teamA@ranking+ as.numeric(bonusReceiver)*3,
                                                           teamB@ranking, 10) else if (type == "WRa")
                                                             newRanking <- computeRkWR_alt(match@scoreA, match@scoreB, 
                                                                                           teamA@ranking + as.numeric(bonusReceiver)*3, 
                                                                                           teamB@ranking, match@weight) else newRanking <- computeRkELOd(match@scoreA, 
                                                                                                                                                         match@scoreB, 
                                                                                                                                                         teamA@ranking+ as.numeric(bonusReceiver)*3,
                                                                                                                                                         teamB@ranking, 10)
  teamA <- updateRanking(teamA, newRanking$rankingA - as.numeric(bonusReceiver)*3, as.POSIXct(match@date, format = "%Y-%m-%d"))
  teamB <- updateRanking(teamB, newRanking$rankingB, as.POSIXct(match@date, format = "%Y-%m-%d"))
  return(list(teamA = teamA, teamB = teamB))
}