Allow grouping with NA in aggregate function

Question

Here is dummy data

temp.df <- data.frame(count = rep(1,6), x = c(1,1,NA,NA,3,10), y=c("A","A","A","A","B","B"))

When I apply aggregate as given below:

aggregate(count ~ x + y, data=temp.df, FUN=sum, na.rm=FALSE, na.action=na.pass)

I get:

   x y count
1  1 A     2
2  3 B     1
3 10 B     1

However, I would like the following output:

   x  y count
1  NA A     2
2  1  A     2
3  3  B     1
4 10  B     1

Hope it makes sense.Thanks in advance.

Answer 1

One option may be to convert the NA to character "NA" (but I am not sure why you need the missing values)

temp.df$x[is.na(temp.df$x)] <- 'NA'
aggregate(count ~ x + y, data=temp.df, FUN=sum, na.rm=FALSE, na.action=na.pass)
#   x y count
#1  1 A     2
#2 NA A     2
#3 10 B     1
#4  3 B     1

Answer 2

Use addNA to treat NA as a distinct level of x.

> temp.df$x <- addNA(temp.df$x)
> aggregate(count ~ x + y, data=temp.df, FUN=sum, na.rm=FALSE, na.action=na.pass)
     x y count
1    1 A     2
2 <NA> A     2
3    3 B     1
4   10 B     1