R/demo_utils.R

In mark-andrews/demopkg: A Demo Package for Demonstrating R Packages

#' Calculate the logarithm of the odds of a probability
#'
#' @export
#' @param p A probability (a value > 0 and < 1)
#' @return The logarithm (to base e) of the probability
#' @examples
#' logit(0.5)
#' logit(0.75)
#' logit(0.25)
logit <- function(p = 0.25){
  log(p/(1-p))
}


#' Calculate the inverse of the logit function
#'
#' @export
#' @param logodds The logarithm (to base e) of some probability
#' @return The probability that is the inverse of the log odds
#' @examples
#' ilogit(3)
#' ilogit(-2)
#' ilogit(0)
ilogit <- function(logodds = 1){
  1/(1 + exp(-logodds))
}


#' Plot a binomial likelihood function
#'
#' @export
#' @param n Number of trials
#' @param m Number of successes
#' @return A ggplot of the likelihood function
#' @examples
#' likelihood(75, 25)
#' likelihood(100, 33)
#' likelihood(50, 10)
#' @import ggplot2
likelihood <- function(n = 100, m = 60){
  data_df <- dplyr::tibble(x = seq(0, 1, length.out = 1000),
                           y = x ^ m * (1 - x) ^ (n - m))

  ggplot(data_df, aes(x = x, y = y)) + geom_line()
}