Not sure if this is the expected behaviour, but split drops custom classes when using the by arg but it keeps them when using the f arg.
library(data.table)
dt = data.table(x = letters[1:10], y = 1:10, z = rnorm(10))
setattr(dt, "class", c("my_class", class(dt)))
# using f
dt |> split(~x) |> lapply(class) |> unlist() |> unique()
#> [1] "my_class" "data.table" "data.frame"
# using by
dt |> split(by = "x") |> lapply(class) |> unlist() |> unique()
#> [1] "data.table" "data.frame"Created on 2025-06-28 with reprex v2.1.1
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Not sure if this is the expected behaviour, but split drops custom classes when using the by arg but it keeps them when using the f arg.
Created on 2025-06-28 with reprex v2.1.1