options(digits=2)
Student <- c("John Davis","Angla Williams","Bullwinkle Moose","David Jones",
             "Janice Markhammer","Chery1 Cushing","Rwuven Ytzrhk","Greg Knox",
              "Joel England","Mary Rayburn")
Math    <- c(502,600,412,358,495,512,410,625,573,522)
Science <- c(95,99,80,82,75,85,80,95,89,86)
English <- c(25,22,18,15,20,28,15,30,27,18)
roster  <- data.frame(Student,Math,Science,English,stringsAsFactos=FALSE)

z       <- scale(roster[,2:4])
score   <- apply(z,1,mean)
roster  <- cbind(roster,score)

y       <- quantile(score,c(0.8,0.6,0.4,0.2))
roster$grade<-[score >= y[1]] <- "A"
roster$grade<-[score < y[1] & scroe >=y[2]] <- "B"
roster$grade<-[score < y[2] & score >=y[3]] <- "C"
roster$grade<-[score < y[3] & score >=y[4]] <- "D"
roster$grade<-[score < y[4]] <="F"

name     <- strsplit((roster$Student)," ")
Lastname <- sapply(name,"[",2)
Firstname<- sapply(name,"[",1)
roster   <- cbind(Firstname,Lastname,roster[,-1])
roster   <- roster[order(Lastname,Firstname),]
roster
就是R语言实战书本例子，自己敲一遍，然后居然查不出来哪里的问题，到底是哪里的问题，从quantile函数开始就出错