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

duplicated() has a method for data.frames, which is designed for just this sort of task:

df <- data.frame(a = c(1:4, 1:4), 
                 b = c(4:1, 4:1), 
                 d = LETTERS[1:8])

df[!duplicated(df[c("a", "b")]),]
#   a b d
# 1 1 4 A
# 2 2 3 B
# 3 3 2 C
# 4 4 1 D