从R中的函数返回和访问对象

Question

I wrote a function in R that returns a list composed of two variables. The function works correctly in that the correct values are returned. The problem, however, is that I can't then access the list for further processing. The code is this:

grinder <- function(x) {

if(x == "BID") {
miles <- 18.4 * n.row
tolls <- 1.8 * n.row

} else if(x == "SPR") {
miles <- 10.8 * n.row
tolls <- 0

} else if (x == "BRI") {
miles <- 3.8 * n.row
tolls <- 0

} else if (x == "GOO") {
miles <- 66.2 * n.row
tolls <- 1.8 * n.row

} else if (x == "MIL") {
miles <- 108
tolls <- 0

} else if (x == "SMH") {
miles <- 94.6 * n.row
tolls <- 2 * n.row

}

mil.tol <- list(miles,tolls)
return(mil.tol)

}

grinder(x)

The correct values are returned, but I can't then access mil.tol to do anything with those values. Nor can I get correct values for miles or tolls. The console returns this:

> mil.tol
Error: object 'mil.tol' not found
> miles

Any suggestions?

Answer 1

miles , tolls and mil.tol are all local to the function and are not returned, but you can assign the output of the function (ie from the return() ) like below to mil.tol:

mil.tol <- grinder(x)

Would recommend also reading this SO post here