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

You can also try aggregating by is.na(a[,2]) instead.

aggregate(a[,1], by=list(is.na(a[,2])), sum)

#   Group.1 x
# 1   FALSE 3
# 2    TRUE 2

If you want a finer distinction than just NA or not, then you may want to define a new variable that uses an previously unused value to denote NA (a factor would be more elegant, but a numeric vector is the simplest):

b <- a[,2]
b[is.na(b)] <- 999
aggregate(a[,1], by=list(b), sum)

#   Group.1 x
# 1       2 3
# 2     999 2