Count of unique elements of each row in a data frame in R

Question

I have a data frame like below:

Group1  Group2  Group3  Group4
A       B       A       B   
A       C       B       A   
B       B       B       B   
A               


        

Answer 1

duplicated in base R:

df$Count <- apply(df,1,function(x) sum(!duplicated(x)))

#  Group1 Group2 Group3 Group4 Count
#1      A      B      A      B     2
#2      A      C      B      A     3
#3      B      B      B      B     1
#4      A      C      B      D     4
#5      A      D      C      A     3