plotProgresskMeans <- function (X, centroids, previous, idx, K, i) {
  
  #   Helper function that displays the progress of
  #   k-Means as it is running. It is intended for use only with 2D data.
  #
  #   plotProgresskMeans(X, centroids, previous, idx, K, i) plots the data
  #   points with colors assigned to each centroid. With the previous
  #   centroids, it also plots a line between the previous locations and
  #   current locations of the centroids.
  #
  
  # Setup the plot
  plot(X, type = "n")
  title(main = sprintf('Iteration number %d', i))
  
  # Plot the examples
  plotDataPoints(X, idx, K)
  
  # Plot the centroids as black x's
  points(centroids, pch = 4, lwd = 2)
  
  # Plot the history of the centroids with lines and points
  for (q in 2:dim(previous)[3]) { # num of centroids so far
    if (all(previous[, , q] == 0)){
      break
    } else{
      for (j in 1:dim(centroids)[1]){
        #num of centroids 3
        lines(rbind(previous[j, ,q - 1], previous[j, , q]), type = "b", pch = 4, lwd = 1.3)
      }    
    }
  }
}