r语言班级成绩向量问题求解 rstudio

score=c(90,78,63,84,36,NA,84,58,80,75,85,72,78,86)
grade=c(3,3,3,4,3,3,3,3,3,3,4,3,4,4)

# 1)
stuNum=length(score);print(stuNum)
testNum=length(score[!is.na(score)]);print(testNum)

# 2)
score[is.na(score)]<-80
print(score)

# 3)
score3<-score[grade==3];print(score3)
score4<-score[grade==4];print(score4)

# 4)
task1<-list(score3,score4)
print(task1)