Remove all unique rows

Question

I am trying to figure out how to remove all unique rows, from a data frame, but if it has a duplicate, I want that to stay in. For Example - I want all columns from this wi

Answer 1

You can do this by creating an index with ave:

df[as.logical(ave(1:nrow(df), df$col1, FUN=function(x) length(x) > 1)), ]

produces

  col1 col2 col3
1    a    A    3
2    a    B    3
3    a    C    1
6    d    A    3
7    d    B    2
8    d    C    1