从函数返回一个对象

Question

如何从函数返回对象，而不是调用对象时提供的输出？

best.mod <- function(d){
  m1 <- lm(Sepal.Length~Sepal.Width, d)
  m2 <- lm(Sepal.Length~Sepal.Width + I(Sepal.Width^2), d)
  ifelse(AIC(m1) < AIC(m2), m1, m2)
}

mod <- best.mod(iris[iris$Species == "setosa",])
class(mod)

Answer 1

问题来自于使用ifelse。这是为了向量化比较。标准的 if ... else 在这里更好:

best.mod <- function(d){
  m1 <- lm(Sepal.Length~Sepal.Width, d)
  m2 <- lm(Sepal.Length~Sepal.Width + I(Sepal.Width^2), d)
  if(AIC(m1) < AIC(m2)) return(m1) else return(m2)
}

mod <- best.mod(iris[iris$Species == "setosa",])
class(mod)
[1] "lm"

注意来自 ?ifelse 的警告:

The mode of the result may depend on the value of test (see the examples), and the class attribute (see oldClass) of the result is taken from test and may be inappropriate for the values selected from yes and no.