Data <- read.delim('http://myweb.uiowa.edu/pbreheny/data/tailgating.txt')

# Create separate data set for each group
DrugYes <- subset(Data, Drug==1)
DrugNo <- subset(Data, Drug==0)

# Do bootstrapping
B <- 10000
medYes <- medNo <- numeric(B)
for (i in 1:B) {
  medYes[i] <- median(sample(DrugYes$Distance, replace=TRUE))
  medNo[i] <- median(sample(DrugNo$Distance, replace=TRUE))
}
Diff <- medNo - medYes

# Bootstrap confidence interval
quantile(Diff, c(.025, .975))

# Some inspection to see what these objects look like
head(medYes)
head(medNo)
hist(Diff, col='gray', border='white', las=1)