Multiple duplicates (2 times, 3 times,…) in R

Question

After searching for a while, I know that this question has not been answered yet. Assume that I have the following vector

v <- c("a", "b", "b", "c","c","c", "d", "d", "d", "d")

How do I find those values having more than 1 duplicates

(should be "c","c","c", "d", "d", "d", "d")

and more than 2 duplicates

(should be "d", "d", "d", "d" )

Function duplicated(v) only returns values having duplicates.

Answer 1

You can generate a table() and then check which elements of v are part of the relevant subset of the table, eg

R> v <- c("a", "b", "b", "c","c","c", "d", "d", "d", "d")
R> tab <- table(v)
R> tab
v
a b c d 
1 2 3 4 
R> v[v %in% names(tab[tab > 2])]
[1] "c" "c" "c" "d" "d" "d" "d"
R> v[v %in% names(tab[tab > 3])]
[1] "d" "d" "d" "d"

Answer 2

I would use ave to write a simple function like this:

myFun <- function(vector, thresh) {
  ind <- ave(rep(1, length(vector)), vector, FUN = length)
  vector[ind > thresh + 1] ## added "+1" to match your terminology
}

Here it is applied to "v":

myFun(v, 1)
# [1] "c" "c" "c" "d" "d" "d" "d"
myFun(v, 2)
# [1] "d" "d" "d" "d"

---

Of course, there is always "data.table":

as.data.table(v)[, N := .N, by = v][N > 1 + 1]$v
# [1] "c" "c" "c" "d" "d" "d" "d"
as.data.table(v)[, N := .N, by = v][N > 2 + 1]$v
# [1] "d" "d" "d" "d"