nansum in R for data.table

Question

Let's start with DT1

library(data.table)
DT1 <- data.table(c(NA, NA, NA, NA, NA),
                  c(1, 1, 1, 1, NA),
                  c(1, 1, 1, 1, NA))
# 1: NA  1  1
# 2: NA  1  1
# 3: NA  1  1
# 4: NA  1  1
# 5: NA NA NA

We also have DT2

DT2 <- data.table(c(NA, NA, NA, NA, NA),
                  c(2, 2, 2, 2, 2),
                  c(2, 2, 2, 2, 2))
# 1: NA  2  2
# 2: NA  2  2
# 3: NA  2  2
# 4: NA  2  2
# 5: NA  2  2

I want to sum the two data.table, so I would get the following result:

# 1: NA  3  3
# 2: NA  3  3
# 3: NA  3  3
# 4: NA  3  3
# 5: NA  2  2

Answer 1

One option is Map

setDT(Map(function(x,y) {x1 <- rowSums(cbind(x,y), na.rm  = TRUE)
           x1[is.na(x) & is.na(y)] <- NA
            x1}, DT1, DT2))[]
#   V1 V2 V3
#1: NA  3  3
#2: NA  3  3
#3: NA  3  3
#4: NA  3  3
#5: NA  2  2