Remove duplicates column combinations from a dataframe in R

Question

I want to remove duplicate combinations of sessionid, qf and qn from the following data

               sessionid             qf        qn         city
1  9         


        

Answer 1

It works if you use duplicated twice:

> df

  a  b c    d
1 1  2 A 1001
2 2  4 B 1002
3 3  6 B 1002
4 4  8 C 1003
5 5 10 D 1004
6 6 12 D 1004
7 7 13 E 1005
8 8 14 E 1006

> df[!(duplicated(df[c("c","d")]) | duplicated(df[c("c","d")], fromLast = TRUE)), ]

a  b c    d
1 1  2 A 1001
4 4  8 C 1003
7 7 13 E 1005
8 8 14 E 1006