typeof(data.frame) shows "list" in R [duplicate]

Question

Can someone clarify why typeof (data.frame) shows list in R? In contrast, class gives expected type. E.g., demonstrate that using the built-in data.frame mtcars.

> typeof(mtcars)
[1] "list"
> class(mtcars)
[1] "data.frame"

Any hints on how to use typeof versus class?

Answer 1

data.frame and data.table are both collections (lists) of items (vectors, if you will), each item of the same length (ie each column is an item in the list, internally to R anyway). This is why unlike in a matrix, columns can have different classes.

Cheers.