R Combine mapply and sapply

Question

I have a function in R that takes in 3 parameters, say foo(x,y,z).

When I call the function, I really have a list of elements for x, and a list for y but only one element for z. If Z was a list, and I wanted to apply foo to each element, mapply(foo, x, y, z) works.

However, since z is not a list, mapply(foo,x,y,z) does not work.

More specifically, if x and y are lists of 3 elements each, the following does work however: mapply(foo, x, y, list(z, z, z)).

Is there a way I can perhaps combine mapply and sapply without me first making z into a list of 3 elements? I want z to just be reused!

Edit 1: I was asked for an example:

mylist1 <- list(c(5,4), c(7,9), c(8,3))
mylist2<- list(c(2,3), c(6,7), c(10,11))
item3 <- matrix(data = 15, nrow = 3, ncol = 3)
foo <- function(x,y,z){
       return(x[1]+y[2]+z[2,2])
}

The following works:

> mapply(foo, mylist1, mylist2, list(item3,item3, item3))
[1] 23 29 34

The following does not work:

mapply(foo, mylist1, mylist2, item3)
Error in z[2, 2] : incorrect number of dimensions

Answer 1

Use the MoreArgs argument to mapply

mapply(foo, x = mylist1, y= mylist2, MoreArgs = list(z = item3))
## [1] 23 29 34

Answer 2

You just have to put the last item in a list, and R will recycle it just fine:

mapply(foo, mylist1, mylist2, list(item3))

Note that the documentation specifically says that the arguments you pass need to be:

arguments to vectorize over (vectors or lists of strictly positive length, or all of zero length)

and you were trying to pass a matrix.