Get the grouping variables

group_vars(x)

Arguments

df <- data.table(
  a = 1:3,
  b = 4:6,
  c = c("a", "a", "b"),
  d = c("a", "a", "b")
)

df %>%
  group_by(c, d) %>%
  group_vars()
#> [1] "c" "d"