if-else结构
语法为
if(cond)statement
if(cond) statement1 else statement2
举一个比较213的例子
> a<-c(1:10)
> if(length(a)<10) print(1) else print(2)
[1] 2
ifelse结构
语法为
ifelse(cond,statement1,statement2)条件为TRUE时执行statement1,否则执行statement2
仍旧是那个213的例子
> ifelse(length(a)<10,print(1),print(2))
[1] 2
[1] 2
switch结构
switch根据一个表达式的值选择语句执行
switch(expr,……)
举一个例子
feelings<-c('sad','afraid')
for (i in feelings)
{print(
switch(i,
happy='I am glad you are happy',
sad='cheer up',
angry='calm down now',
afraid='there is nothing to fear'))}
> source('E:/Rworking/switch.R')
[1] "cheer up"
[1] "there is nothing to fear"