R Recode variable for all observations that do not occur more than once

Question

I have a simple dataframe that looks like the following:

Observation X1 X2 Group
1           2   4   1
2           6   3   2
3           8   4   2
4           1   3   3
5           2   8   4
6           7   5   5
7           2   4   5

How can I recode the group variable such that all non-recurrent observations are recoded as "unaffiliated"?

The desired output would be the following:

Observation X1 X2 Group
1           2   4   Unaffiliated
2           6   3   2
3           8   4   2
4           1   3   Unaffiliated
5           2   8   Unaffiliated
6           7   5   5
7           2   4   5

Answer 1

One way could be first grouping then checking for maximum of row number and finishing with an ifelse:

library(dplyr)

df %>% 
  group_by(Group) %>% 
  mutate(Group = ifelse(max(row_number()) == 1, "Unaffiliated", as.character(Group))) %>% 
  ungroup()

  Observation    X1    X2 Group       
        <int> <int> <int> <chr>       
1           1     2     4 Unaffiliated
2           2     6     3 2           
3           3     8     4 2           
4           4     1     3 Unaffiliated
5           5     2     8 Unaffiliated
6           6     7     5 5           
7           7     2     4 5