Remove both rows that duplicate in R

Question

I'm trying to remove all rows that have a duplicate value. Hence, in the example I want to remove both rows that have a 2 and the three rows that have 6 under the x column. I have tried df[!duplicated(xy$x), ] however this still gives me the first row that duplicates, where I do not want either row.

    x <- c(1,2,2,4,5,6,6,6)
    y <- c(1888,1999,2000,2001,2004,2005,2010,2011)
    xy <- as.data.frame(cbind(x,y))
    xy
    x    y
  1 1 1888
  2 2 1999
  3 2 2000
  4 4 2001
  5 5 2004
  6 6 2005
  7 6 2010
  8 6 2011

What I want is

    x     y
    1  1888
    4  2001
    5  2004

Any help is appreciated. I need to avoid specifying the value to get rid of since I am dealing with a dataframe with thousands of records.

Answer 1

You can count and include only the singletons

xy[1==ave(xy$x,xy$x,FUN=length),]

  x    y
1 1 1888
4 4 2001
5 5 2004

Answer 2

we can do

xy[! xy$x %in% unique(xy[duplicated(xy$x), "x"]), ]
#  x    y
#1 1 1888
#4 4 2001
#5 5 2004

as

unique(xy[duplicated(xy$x), "x"])

gives the values of x that are duplicated. Then we can just filter those out.