Aggregate by NA in R

Question

Does anybody know how to aggregate by NA in R.

If you take the example below

a <- matrix(1,5,2)
a[1:2,2] <- NA
a[3:5,2] <- 2
aggregate(a[,1]         


        

Answer 1

Using sqldf:

a <- as.data.frame(a)
sqldf("SELECT V2 [Group], SUM(V1) x 
      FROM a 
      GROUP BY V2")

Output:

  Group x
1    NA 2
2     2 3

stats package

A variation of AdamO's proposal:

data.frame(xtabs( V1 ~ V2 , data = a,na.action = na.pass, exclude = NULL))

Output:

    V2 Freq
1    2    3
2     2