R/b.R

In jvcasill/lingStuff: Tools and Gems for Linguistics Related Research

#' A b function
#'
#' This function allows you to calculate b from a vector hits 
#' and a vector a false alarms.
#'
#' @param data A data frame.
#' @param h A vector of hits (0 = miss, 1 = hit).
#' @param f A vector of false alarms (0 = correct rejection, 1 = false alarm).
#' @keywords b prime
#' @export
#' @examples
#' # Create some data
#' set.seed(1); library(dplyr)
#' axb <- data.frame(subj = sort(rep(1:10, each = 20, times = 10)),
#'                   group = gl(2, 1000, labels = c("g1", "g2")),
#'                   hit = c(rbinom(1000, size = c(0, 1), prob = .8), 
#'                           rbinom(1000, size = c(0, 1), prob = .6)),
#'                   fa =  c(rbinom(1000, size = c(0, 1), prob = .3), 
#'                           rbinom(1000, size = c(0, 1), prob = .4))
#' )
#' 
#' # Calculate b on entire data frame
#' b(axb, hit, fa)
#'
#' # Calculate b for each subject
#' # by group, plot it, and run a 
#' # linear model
#' axb %>%
#'   group_by(subj, group) %>%
#'   summarize(b = b(., hit, fa)) %T>%
#'  {
#'   plot(b ~ as.numeric(group), data = ., 
#'        main = "b as a function of group", xaxt = "n", 
#'        xlab = "Group", ylab = "b")
#'   axis(1, at = 1:2, labels = c("g1", "g2"))
#'   abline(lm(b ~ as.numeric(group), data = .), col = "red")
#'  } %>%
#'  lm(b ~ group, data = .) %>%
#'  summary()

b <- function(data, h, f){
    if(!is.data.frame(data)) {
    stop('I am so sorry, but this function requires a dataframe\n',
         'You have provided an object of class: ', class(data)[1])
    }

    # Make columns of dataframe available w/o quotes
    arguments <- as.list(match.call())
    hits = eval(arguments$h, data)
    fas = eval(arguments$f, data)

    hRate = mean(hits)
    faRate = mean(fas) 

    if(faRate <= .5 & hRate >= .5)
      {
        b <- (5 - 4 * hRate) / (1 + 4 * faRate)
      } else if(faRate <= hRate & hRate <= .5)
      {
        b <-(hRate^2 + hRate) / (hRate^2 + faRate) 
      } else { 
        b <- ((1 - faRate)^2 + (1 - hRate)) / ((1 - faRate)^2 + (1 - faRate))
      } 
      return(b)
}