R: how to check if there are multiple names with the given id in a dataframe

Question

I have a R data like the following:

id = c(1,1,1,2,2,4,4,3,3,3)
buyernames = c("ann","ann","bo","celine","celine","mary","lily","john","john","john")
data = cbind(id,buyernames)
#id  buyernames
#[1,] "1" "ann"     
#[2,] "1" "ann"     
#[3,] "1" "bo"      
#[4,] "2" "celine"  
#[5,] "2" "celine"  
#[6,] "4" "mary"    
#[7,] "4" "lily"    
#[8,] "3" "john"    
#[9,] "3" "john"    
#[10,] "3" "john"    

ID is numeric. What I want to know is if there are ids that are associated with different names. If so, what are the ids and names.

desired output - a data like the following:

   id   buyernames
    1    ann
    1    bo
    4    mary
    4    lily

Any insight would be greatly appreciated.

Answer 1

The unique function can eliminate duplicate rows, and the duplicated function can be used to identify duplicate ids after duplicate rows are removed. So, the following should work:

id = c(1,1,1,2,2,4,4,3,3,3)
buyernames = c("ann","ann","bo","celine","celine","mary","lily","john","john","john")
data = cbind(id,buyernames)

D <- unique(data.frame(data))           # get unique rows
dupids <- with(D, id[duplicated(id)])   # duplicate ids
subset(D, id %in% dupids)               # rows for duplicate ids