wish list: generalized apply

On Dec 8, 2016, at 12:09 PM, John P. Nolan <jpnolan at american.edu> wrote:

Dear All,

I regularly want to "apply" some function to an array in a way that the arguments to the user function depend on the index on which the apply is working.  A simple example is:

A <- array( runif(160), dim=c(5,4,8) )
x <- matrix( runif(32), nrow=4, ncol=8 ) 
b <- runif(8)
f1 <- function( A, x, b ) { sum( A %*% x ) + b } 
result <- rep(0.0,8) 
for (i in 1:8) {
 result[i] <- f1( A[,,i], x[,i] , b[i] )
}

This works, but is slow.  I'd like to be able to do something like:
   generalized.apply( A, MARGIN=3, FUN=f1, list(x=x,MARGIN=2), list(b=b,MARGIN=1) ), where the lists tell generalized.apply to pass x[,i] and b[i] to FUN in addition to A[,,i].  

Does such a generalized.apply already exist somewhere?  While I can write a C function to do a particular case, it would be nice if there was a fast, general way to do this.