ROC curves for each class of the MNIST 10-class classifier

rwml-R_figure4_20.R

library(ROCR)
library(dplyr)

mnistResultsDF <- data.frame(actual = mnistTest$label,
                             fit = mnist.kknn$fit,
                             as.data.frame(mnist.kknn$prob))

plotROCs <- function(df, digitList) {
  firstPlot <- TRUE
  legendList <- NULL
  for (digit in digitList) {
    dfDigit <- df %>%
      filter(as.character(actual) == as.character(digit) |
               as.character(fit) == as.character(digit))  %>%
      mutate(prediction = (as.character(actual) == as.character(fit)))
    
    pred <- prediction(dfDigit[,digit+3], dfDigit$prediction)
    perf <- performance(pred, "tpr", "fpr")
    auc <- performance(pred, "auc")
    legendList <- append(legendList, 
                         paste0("Digit: ",digit,", AUC: ",
                                round(auc@y.values[[1]], digits = 4)))
    if (firstPlot == TRUE) {
      plot(perf, colorize = FALSE, lty = digit+1, col = digit+1)
      firstPlot <- FALSE  
    } else {
      plot(perf, colorize = FALSE, add = TRUE, lty = digit+1, col = digit+1)
    }
  }
  legend(x=0.4, y=0.6,
         legend = legendList,
         col = 1:10,
         lty = 1:10,
         bty = "n")
}

plotROCs(mnistResultsDF, 0:9)