Given two data frames
df1 = data.frame(CustomerId=c(1:6),Product=c(rep("Toaster",3),rep("Radio",3)))
df2 = data.frame(CustomerId=c(2,4,6),State=c(rep("Alabama",2),rep("Ohio",1)))
> df1
CustomerId Product
1 Toaster
2 Toaster
3 Toaster
4 Radio
5 Radio
6 Radio
…