I need a solution that shows me which rows are identical but I can't find a clever solution (a solution without a bunch of complex loops). I would prefer a `data.table` solution.
What I want to have is a list with line numbers that have the identical entries.

An example:

```
library(data.table)
Data <- data.table(A = c("a", "a", "c"), 
                   B = c("A", "A", "B"))

```

The first and the second line are identical.
My desired output:

```
[[1]]
[1] 1 2

[[2]]
[1] 3

```