如何找出哪个方法被分派到 S3 对象？

Question

How can I find out which method is being dispatched when I apply a function to an S3 object?

For example, if I run the code

df <- data.frame(list("a" = c(1,2,3)), "b" = c(7,8,9))

print(df)

I think the method print.data.frame is being dispatched because it shows up when running methods(class="data.frame")

Is there a way verify this? Such as a function that takes in print and data.frame and outputs the method used?

Answer 1

The sloop package can show you more details. For example

sloop::s3_dispatch(print(df))
# => print.data.frame
#  * print.default

this shows you all the possible matches, and highlights the one that was actually used ( print.data.frame )

But in general you need to look at the class() of the object you pass to the function. The first class that matches up with the methods() listed for the function will be the one called. If you want to see the code of the function that would be used, you could use

getS3method("print", "data.frame")