Why doesn't setDT have any effect in this case?

Question

Consider the following code

library(data.table) # 1.9.2
x <- data.frame(letters[1:2]) 
setDT(x) 
class(x)
## [1] \"data.table\" \"data.frame\"


        

Answer 1

setDT changes the data.frame and returns it invisibly. Since you don't save this data.frame, it is lost. All you need to do is somehow save the data.frame, so that the data.table is also saved. E.g.

setDT(y <- data.frame(x)) 
class(y)
## [1] "data.table" "data.frame"

or

z <- setDT(data.frame(x))
class(z)
## [1] "data.table" "data.frame"