ROC plot and AUC calculation the tidy way - by David Robinson (@drob) tweeted at 5:22 PM on Tue, Nov 29, 2016: Using tidyverse tools to calculate AUC and plot ROC curves #rstats https://t.co/BYJcKXJwoe (https://twitter.com/drob/status/803635156841943040?s=03)

roc_auc_tidy.R

library(tidyverse)
theme_set(theme_minimal())

roc <- iris %>% 
  gather(Metric, Value, -Species) %>%
  mutate(Positive = Species == "virginica") %>%
  group_by(Metric, Value) %>%
  summarise(Positive = sum(Positive),
            Negative = n() - sum(Positive)) %>%
  arrange(-Value) %>%
  mutate(TPR = cumsum(Positive) / sum(Positive),
         FPR = cumsum(Negative) / sum(Negative))

roc %>% group_by(Metric) %>%
  summarise(AUC = sum(diff(FPR) * na.omit(lead(TPR) + TPR)) / 2)


ggplot(roc, aes(FPR, TPR, color = Metric, frame = FPR)) +
  geom_line() +
  geom_abline(lty = 2)