Subsetting a data frame to the rows not appearing in another data frame

Question

I have a data frame A with observations

    Var1   Var2  Var3
     1       3    4
     2       5    6
     4       5    7
     4       5    8
     6       7    9         


        

Answer 1

Using data.table you could do an anti-join as follows:

library(data.table)
setDT(df1)[!df2, on = names(df1)]

which gives the desired result:

   Var1 Var2 Var3
1:    4    5    7
2:    4    5    8
3:    6    7    9