cf <- function(score,P50,P75){
  if (score<P50) {
    return(3)
  } else if (score>=P50 & score<P75) {
    return(2)
  } else {
    return(1)
  }
}


classp <- NULL
for (i in 1:dim(pdata)[1])   {
  classp[i] <- cf(score=pdata$平均成績[i], P50 = pdata$P50[i],P75 = pdata$P75[i])
}
classp