Remove all entries that occur more than once

New to Julia
2

Yeah, Base.unique returns distinct values rather than unique ones.

julia> filter(x->x.nrow ==1, combine(groupby(firstnames, :name), nrow, :gender))
1×3 DataFrame
 Row │ name    nrow   gender 
     │ String  Int64  String 
─────┼───────────────────────
   1 │ Anton       1  M