1 控制流

1.1 重复和循环

方式一：for()

for (i in 1:10)  print("hello")

方式二：while()

while(i>0){

  print("hello")

  i<-i-1

}

 

1.2 条件执行

方式一：if-else结构

if (is.character(roster$grade)) roster$grade<-as.factor(roster$grade)

 

if (!is.factor(roster$grade)) roster$grade<-as.factor(roster$grade) else print("grade already is a factor")

 

score<-0.4

ifelse(score>0.5,print("Passed"),print("Failed"))

 

方式二：switch结构

feel<-c("sad","afraid")

for (i in feel)

  print(

    switch (i,

           happy = "I am glad you are happy",

           afraid="There is nothing to fear",

           sad="Cheer up",

           angry="Clam down"

          )

      )

 

3 用户自编函数

3.1 if-else结构自编函数

（1）自定义函数

myfun<-function(x,parametric=T,print=F){

  if(parametric){

    center<-mean(x);spread<-sd(x)    

  }else{

    center<-median(x);spread<-mad(x)               #mad是中位数绝对偏差

  }

  

  if(print & parametric){

    cat("Mean=",center,"\n","SD=",spread,"\n")

  }else if(print & parametric){

    cat("Median=",center,"\n","MAD=",spread,"\n")

  }

  

  result<-list(center=center,spread=spread)

  return(result)

}

（2）传递参数

set.seed(123)  #设置随机种子，保持生成的随机数不变

x<-rnorm(500)  #生成500个随机数

y<-myfun(x)

 

y1<-myfun(x,parametric=F,print=T)