Counting observations according to the number of variables missing

Question

I would like to count the rows of a data frame, according to the number of variables that are missing. So for example in the data frame below I would like the code to return

Answer 1

table(rowSums(is.na(dt)))
#0 1 2 3 
#3 5 1 1 

If you really need the last 0 (four NAs):

tabulate(factor(rowSums(is.na(dt))), nbins = ncol(dt)+1)
#[1] 3 5 1 1 0