R/entropy.R

In soodoku/goji: Misc. functions for handling simple things

#' Calculate Entropy
#'
#' Max. for now 4 categories
#' 
#' Takes a vector and number of categories
#'  
#' @param x vector
#' @param n can be 2 or 4 
#' @return recoded vector
#' @export
#' @examples
#' x <- c(1,2,3); entropy(x,2)

entropy <- function(x, n) {

  entropy <- NA

  ent1 <- ent2 <- ent3 <- ent4 <- 0

  if (sum(x, na.rm = T) == 0 | length(table(round(x, 2))) == 0) {
    entropy <- NA
  }

  if (length(table(round(x, 2))) > 0) {

    p <- table(round(x, 2)) / length(x)

    if (n == 2) {
      p1 <- p[1]
      p2 <- 1 - p1

      if (p1 == 0) {
        ent1 <- 0
      } else {
        ent1 <- p1 * log2(p1)
      }
      if (p2 == 0) {
        ent2 <- 0
      } else {
        ent2 <- p2 * log2(p2)
      }
      entropy <- - (ent1 + ent2)
    }

    if (n == 4) {

      if (p[1] == 0) {
        ent1 <- 0
      } else {
        ent1 <- p[1] * log2(p[1])
      }
      if (!is.na(p[2]) & p[2] == 0){
        ent2 <- 0
      } else {
        ent2 <- p[2] * log2(p[2])
      }
      if (!is.na(p[3]) & p[3] == 0){
        ent3 <- 0
      } else {
        ent3 <- p[3] * log2(p[3])
      }
      if (!is.na(p[4]) & p[4] == 0){
        ent4 <- 0
      } else {
        ent4 <- p[4] * log2(p[4])
      }
      entropy <- - (ent1 + ent2 + ent3 + ent4)
     }
    }
    entropy
}