R/get_mode.R

In gpilgrim2670/SwimmeR: Data Import, Cleaning, and Conversions for Swimming Results

#' Find the mode (most commonly occurring) element of a list
#'
#' Determines which element of list appears most frequently.  Based on
#' \code{base::which.max()}, so if multiple values appear with the same
#' frequency will return the first one.  Ignores \code{NA} values. In the
#' context of swimming data is often used to clean team names, as in the Lilly
#' King example below.
#'
#' @param x A list.  \code{NA} elements will be ignored.
#' @param type a character string of either \code{"first"} or \code{"all"} which
#'   determines behavior for ties.  Setting \code{type = "first"} (the default)
#'   will return the element that appears most often and appears first in list
#'   \code{x}.  Setting \code{type = "all"} will return all elements that appear
#'   most frequently.
#' @return the element of \code{x} which appears most frequently.  Ties go to
#'   the lowest index, so the element which appears first.
#'
#' @examples a <- c("a", "a", "b", "c")
#' get_mode(a)
#' ab <- c("a", "a", "b", "b", "c") # returns "a", not "b"
#' get_mode(ab)
#' #' ab <- c("a", "a", "b", "b", "c") # returns "a" and "b"
#' get_mode(ab, type = "all")
#' a_na <- c("a", "a", NA, NA, "c")
#' get_mode(a_na)
#' numbs <- c(1, 1, 1, 2, 2, 2, 3, NA)
#' get_mode(numbs, type = "all")
#'
#' Name <- c(rep("Lilly King", 5))
#' Team <- c(rep("IU", 2), "Indiana", "IUWSD", "Indiana University")
#' df <- data.frame(Name, Team, stringsAsFactors = FALSE)
#' df$Team <- get_mode(df$Team)
#'
#' @export

get_mode <- function(x, type = "first") {
  # returns first element that appears most often (a tie breaking method)
  if(type == "first") {
    unique_x <- unique(x[!is.na(x)])
    unique_x[which.max(tabulate(match(x, unique_x)))]
  # returns all elements that appear most often (doesn't break ties, just returns all tied elements)
  } else if (type == "all") {
    unique_x <- unique(x[!is.na(x)])
    tab <- tabulate(match(x, unique_x))
    unique_x[tab == max(tab)]
  } else {
    stop("Please set type to either 'first' or 'all'")
  }
}