Finding ALL duplicate rows, including “elements with smaller subscripts”

Question

R\'s duplicated returns a vector showing whether each element of a vector or data frame is a duplicate of an element with a smaller subscript. So if rows 3, 4,

Answer 1

You need to assemble the set of duplicated values, apply unique, and then test with %in%. As always, a sample problem will make this process come alive.

> vec <- c("a", "b", "c","c","c")
> vec[ duplicated(vec)]
[1] "c" "c"
> unique(vec[ duplicated(vec)])
[1] "c"
>  vec %in% unique(vec[ duplicated(vec)]) 
[1] FALSE FALSE  TRUE  TRUE  TRUE