R Language 流程控制 if(cond)statement if-else if(cond)statement1 else statement2 ifelse if(cond,statement1,statement2) if(FALSE) 一个表达式，不能是NA X message("This won't execute...") }else +{ message("and you'll get an error before you reach this." +} and you'll get an error before you reach this. ifelse(rbinom(10,1,0.5),"Head","Tail") [1]"Tail""Head""Head""Head""Tail""Head""Head""Tail" [9]"Tail""Tail"if-else if(cond) statement if(cond) statement1 else statement2 ifelse if(cond, statement1, statement2) Ӟӻᤒᬡୗ҅ӧᚆฎNA R Language 流程控制