gao_sample.txt

### Professor X. Gao's Sample R Code
### Original Source can be found at https://xingao.info.yorku.ca/files/2020/01/math3333projectsamplecode.txt
### Photograph examples

## Read in the library and metadata
library(jpeg)
pm <- read.csv("C:\\Users\\xingao\\Documents\\teaching\\winter2020\\math3333\\photoMetaData.csv")
n <- nrow(pm)

trainFlag <- (runif(n) > 0.5)
y <- as.numeric(pm$category == "outdoor-day")

X <- matrix(NA, ncol=3, nrow=n)
for (j in 1:n) {
  img <- readJPEG(paste0("C:\\Users\\xingao\\Documents\\teaching\\winter2020\\math3333\\columbiaImages\\columbiaImages\\",pm$name[j]))
  X[j,] <- apply(img,3,median)
  print(sprintf("%03d / %03d", j, n))
}



# build a glm model on these median values
out <- glm(y ~ X, family=binomial, subset=trainFlag)
out$iter
summary(out)

# How well did we do?
pred <- 1 / (1 + exp(-1 * cbind(1,X) %*% coef(out)))
y[order(pred)]
y[!trainFlag][order(pred[!trainFlag])]

mean((as.numeric(pred > 0.5) == y)[trainFlag])
mean((as.numeric(pred > 0.5) == y)[!trainFlag])

## ROC curve (see lecture 12)
roc <- function(y, pred) {
  alpha <- quantile(pred, seq(0,1,by=0.01))
  N <- length(alpha)

  sens <- rep(NA,N)
  spec <- rep(NA,N)
  for (i in 1:N) {
    predClass <- as.numeric(pred >= alpha[i])
    sens[i] <- sum(predClass == 1 & y == 1) / sum(y == 1)
    spec[i] <- sum(predClass == 0 & y == 0) / sum(y == 0)
  }
  return(list(fpr=1- spec, tpr=sens))
}

r <- roc(y[!trainFlag], pred[!trainFlag])
plot(r$fpr, r$tpr, xlab="false positive rate", ylab="true positive rate", type="l")
abline(0,1,lty="dashed")

# auc
auc <- function(r) {
  sum((r$fpr) * diff(c(0,r$tpr)))
}
glmAuc <- auc(r)
glmAuc