如何读取数据帧的summary()代码?

I have a data frame and I want to learn how the summary generates it's information. Specifically, how does summary generate a count for the number of elements in each level of a factor. I can use summary, but I want to learn how to work with factors better. When I try ?summary, I just get the general info. Is this impossible because it is in bytecode?I have a data frame and I want to learn how the