用于在向量中查找区间总和的 R 函数神秘地返回数字（0），但手动工作正常

Question

I made the following function for finding the sum of all the intervals in a sorted numeric vector:

sum.intervals <- function(x){
        x <- sort(x)
        acc <- 0
        for( i in 1:length(x) - 1 ){
            acc <- acc + x[i + 1] - x[i]
        }
        return(acc)
    }

When trying to use it, I expect a scalar value, but instead get numeric(0) :

x <- c(5, 2, 7, 3)
y <- sum.intervals(x)
y
#numeric(0)

However, when performing the iterations manually the idea works fine:

x <- sort(x)
acc <- 0

i <- 1
acc <- acc + x[i + 1] - x[i]

i <- 2
acc <- acc + x[i + 1] - x[i]

i <- 3
acc <- acc + x[i + 1] - x[i]

acc
#5

What is wrong with the function?

Answer 1

1:length(x) - 1 should be 1:(length(x) - 1) . You are subtracting 1 from every element in the vector.

Answer 2

Do you really need a loop here? Just do:

 sum(diff(sort(x)))

Answer 3

We can do this without a loop as well

sum( x[-1] - x[-length(x)])
#[1] 5