R/demo_utils.R

In nikdraka/demopkg: A Demo Package for Demonstrating R Packages

#' Calculate the logarithm of the odds of a probability
#'
#' @export
#' @param p A probability (a values > 0 and less than 1)
#' @return The logarithm (to base e) of the probability
#' @examples
#' logit(0.5)
#' logit(0.75)
#' logit(0.25)

logit <- function(p) {
  log(p/(1-p))
}

#' Calculate the inverse of the logit function
#'
#' @export
#' @param logodds The logarithm (to base e) of some probabilities
#' @return The probability that is the inverse of the log odds
#' @examples
#' ilogit(3)
#' ilogit(-2)
#' ilogit(0)

ilogit <- function(logodds) {
  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(100, 60)
#' likelihood(75, 25)
#' likelihood(100, 33)
#' @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()
}