How to implement coalesce efficiently in R

Question

Background

Several SQL languages (I mostly use postgreSQL) have a function called coalesce which returns the first non null column element for each row. This can b

Answer 1

A very simple solution is to use the ifelse function from the base package:

coalesce3 <- function(x, y) {

    ifelse(is.na(x), y, x)
}

Although it appears to be slower than coalesce2 above:

test <- function(a, b, func) {

    for (i in 1:10000) {

        func(a, b)
    }
}

system.time(test(a, b, coalesce2))
user  system elapsed 
0.11    0.00    0.10 

system.time(test(a, b, coalesce3))
user  system elapsed 
0.16    0.00    0.15 

---

You can use Reduce to make it work for an arbitrary number of vectors:

coalesce4 <- function(...) {

    Reduce(coalesce3, list(...))
}