An example of how to use mapply() to evaluate a function requiring more than one input over a matrix or array.

apply with multiple input functions

X <- cbind(1:5, 6:10)

G <- 1:5


my.fun <- function(x,y){return(x+y)}


# ----------------------------------
# Loop example
loop.output <- double(length(G))

for (i in 1:length(G)){
  loop.output[i] <- my.fun(X[i,1], X[i,2]) 
}

print(loop.output)

# ----------------------------------
# can we do this with aggregate()
# or tapply() or similar instead?

# YES! we can.. with mapply()
mapply.output <- mapply(my.fun, X[,1], X[,2])