I have the following code in R:
a <- 2
evaluate <- function(x){
b <- 2*x
c <- 3*x
d <- 4*x
out <- list("b" = b, "c" = c, "d" = d)
return(out)
}
evaluate(a)
I obtain something like
$b
[1] 4
$c
[1] 6
$d
[1] 8
How can I compute something like b + c + d ?
so many options
# with
with(evaluate(a), b + c + d)
[1] 18
# unlist the unnamed output object
sum(unlist(evaluate(a)))
[1] 18
# subset a named output object
result <- evaluate(a)
result$b + result$c + result$d
[1] 18
# subset an unnamed output object
evaluate(a)$b + evaluate(a)$c + evaluate(a)$d
[1] 18
# custom function with fancy arguments
f <- function(...) {
args <- unlist(...)
sum(args)
}
f(evaluate(a))
[1] 18
Also, +1 from: @Gregor (double-bracket list subsetting)
result[["b"]] + result[["c"]] + result[["d"]]
[1] 18
result[["b"]] + result[["c"]] + result[["d"]]
sum(unlist(evaluate(a)[c("b","c","d")])) but your with() option is my favorite.
b + c + d. This was only an example. What I wanted was to use b, c, or d in other computations. So making result <- evaluate(a) and then using result$b is the answer that I needed.In R you can access list members using $ operator, followed by member name so, in your code, for example:
result = evaluate(a)
result$b + result$c + result$d
Your function returns a list. You could return a vector and then use the sum() function to compute the sum of the elements in the vector. If you must use a list, the 'Reduce()` function can work.
l <- list(2, 3, 4)
v <- c(2,3,4)
sum(v) # returns 9
Reduce("+", l) # returns 9
out <- list("b" = b, "c" = c, "d" = d)should beout <- sum(b,c,d)