Remove pair duplicates from two columns in a data table

Question

Let DT be a 4 x 2 data table with two columns, X and Y, and the following values:

X|Y
---
1 2
2 1
3 4
4 3

I want to remove duplicated pairs from the data table, namely row 2 and 4 in DT.

Answer 1

One option could be:

df[!duplicated(paste0(pmax(X, Y), pmin(X, Y))), ]

   X Y
1: 1 2
2: 3 4

The same with dplyr:

df %>%
 group_by(ID = paste0(pmax(X, Y), pmin(X, Y))) %>%
 slice(1)

Or with base R:

df[!duplicated(with(df, paste0(pmax(X, Y), pmin(X, Y)))), ]