r - Why does the default S3 method gets called when I pass a vector to the method and the vector S3 method is implemented?

Question

I have defined the following in R:

plotWaterfall         <- function(x, ...) UseMethod("plotWaterfall")
plotWaterfall.default <- function(x, ...) {print("Default method does nothing")}
plotWaterfall.vector  <- function(x, ...) {print("Vector method does something")}

Now if I test the following example:

x<-c(1,2,3)
plotWaterfall(x)

it will print "Default method does nothing" indicating that the S3 framework matches the default method instead of the vector method. Now why is that?

Answer 1

这是因为你的向量的类是numeric. 所以你必须这样做：

plotWaterfall.numeric  <- function(x, ...) {print("Numeric vector")}

plotWaterfall(x)
[1] "Numeric vector"

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您可以使用以下函数确定对象的类class()：

class(x)
[1] "numeric"

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帮助中描述了此行为?UseMethod：

方法分派基于泛型函数的第一个参数的类或作为 UseMethod 的参数提供的对象的类