invisible(x)
invisible makes its argument (temporarily) invisible.
This can be useful whwn it is desired to have functions
return values which can be assigned, but which do not
print when they are not assigned.
Examples
> f1 <- function(x) x
> f2 <- function(x) invisible(x)
> f1(5) # 5 is returned and printed
[1] 5
> f2(5) # 5 is returned but not printed
>