1 控制流
1.1 重復和循環
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 條件執行
方式一：if-else結構
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結構
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 用戶自編函數
3.1 if-else結構自編函數
（1）自定義函數
myfun<-function(x,parametric=T,print=F){
if(parametric){
center<-mean(x);spread<-sd(x)
}else{
center<-median(x);spread<-mad(x) #mad是中位數絕對偏差
}
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）傳遞參數
set.seed(123) #設置隨機種子，保持生成的隨機數不變
x<-rnorm(500) #生成500個隨機數
y<-myfun(x)
y1<-myfun(x,parametric=F,print=T)
