R/implied_odds.R

In papagorgio23/bettoR: Sports Betting Tools

#' @title Probability of Winning Conversion to Odds (American Odds)
#'
#' @description This function provides the fair odds for a given win probability for a given bet.
#'
#' @param prob Probability of winning a bet
#' @param type Type of odds. Possible values are:
#' * `all`, All types
#' * `us`, American Odds
#' * `dec`, Decimal Odds
#' * `frac`, Fractional Odds
#'
#'
#' @return odds American Odds of that bet
#'
#' @examples implied_odds(0.4)
#' @examples implied_odds(0.5238095, type = "all")
#' @examples implied_odds(c(0.3, 0.2, 0.909, 0.7143), type = "dec")
#' @examples implied_odds(c(0.3, 0.2, 0.95, 0.7), type = "frac")
#'
#' @export
implied_odds <- function(prob, type = "us") {
  ## Error Handling
  if (!is.numeric(prob)) {
    stop("Probabilities must be numeric")
  }
  if (!type %in% c("all", "us", "frac", "dec")) {
    stop("type must be either: ('all', 'us', 'dec', 'frac')")
  }
  if (type == "all") {
    us <- prob
    us[] <- NA_real_
    us[which(prob > 0.5)] <-
      prob[which(prob > 0.5)] / (1 - prob[which(prob > 0.5)]) * -100
    us[which(prob <= 0.5)] <-
      (1 - prob[which(prob <= 0.5)]) / prob[which(prob <= 0.5)] * 100

    dec <- prob
    dec[] <- NA_real_
    dec[which(prob < 1)] <- 1 / prob[which(prob < 1)]

    frac <- dec - 1
    frac <- MASS::fractions(frac)

    odds <- data.frame(
      Decimal = dec,
      American = round(us),
      Fraction = as.character(frac),
      `Implied Probability` = prob
    )
  }
  if (type == "us") {
    odds <- prob
    odds[] <- NA_real_
    odds[which(prob > 0.5)] <-
      prob[which(prob > 0.5)] / (1 - prob[which(prob > 0.5)]) * -100
    odds[which(prob <= 0.5)] <-
      (1 - prob[which(prob <= 0.5)]) / prob[which(prob <= 0.5)] * 100
    odds <- round(odds)
  }
  if (type == "dec") {
    odds <- prob
    odds[] <- NA_real_
    odds[which(prob < 1)] <- 1 / prob[which(prob < 1)]
  }
  if (type == "frac") {
    odds <- prob
    odds[] <- NA_real_
    odds[which(prob < 1)] <- 1 / prob[which(prob < 1)]
    odds <- odds - 1
    odds <- MASS::fractions(odds)
  }
  return(odds)
}