R/entry-probabilities.R

In coalitions: Bayesian "Now-Cast" Estimation of Event Probabilities in Multi-Party Democracies

#' Get probabilities to enter the parliament.
#'
#' @inheritParams get_seats
#' @param dirichlet.draws Matrix or data frame containing draws from
#' the posterior (see \code{\link{draw_from_posterior}}).
#' @return Vector of (named) entry probabilities.
#' @seealso \code{\link{draw_from_posterior}}
#' @keywords internal
#' @examples
#' library(coalitions)
#' library(dplyr)
#' # get the latest survey for a sample of German federal election polls
#' surveys <- get_latest(surveys_sample)
#' # use 100 simulations for a fast runtime
#' surveys <- surveys %>% mutate(draws = purrr::map(survey, draw_from_posterior, nsim = 100),
#'                               entryProbs = purrr::map(draws, get_entryprobability))
#' surveys$entryProbs
#' @export
get_entryprobability <- function(dirichlet.draws, hurdle = 0.05) {

  colSums(dirichlet.draws >= hurdle) / nrow(dirichlet.draws)

}