R/elbow_finder.R

In atousaz/Dcongestion: Spatiotemporal congestion detection

#' @title Elbow finder.
#' @name Elbow finder
#'
#' @param two dimentional space
#' @return Elbow cut of point
#' @author Atousa Zarindast

#' @export
#' @return cut of point


elbow_finder <- function(x_values, y_values) {
  # Max values to create line
  max_x_x <- max(x_values)
  max_x_y <- y_values[which.max(x_values)]
  max_y_y <- max(y_values)
  max_y_x <- x_values[which.max(y_values)]
  max_df <- data.frame(x = c(max_y_x, max_x_x), y = c(max_y_y, max_x_y))

  # Creating straight line between the max values
  fit <- lm(max_df$y ~ max_df$x)

  # Distance from point to line
  distances <- c()
  for(i in 1:length(x_values)) {
    distances <- c(distances, abs(coef(fit)[2]*x_values[i] - y_values[i] + coef(fit)[1]) / sqrt(coef(fit)[2]^2 + 1^2))
  }

  # Max distance point
  x_max_dist <- x_values[which.max(distances)]
  y_max_dist <- y_values[which.max(distances)]

  return(c(x_max_dist, y_max_dist))
}