Question

I have two snippets of code which I would have expected to behave the same, but they don’t:

  position <- function(t) {
    coordinates <- c(cosh(t), sinh(t))

    return(coordinates[1])
  }

and

  position <- function(t) {
    coordinates <- c(cosh(t), sinh(t))

    return(cosh(t))
  }

I use the function position to plot a curve. With the first snippet the curve is not plotted. With the second snippet the curve is plotted.

What is the functional difference between the two snippets, and why?

Answer 1

The result of

coordinates <- c(cosh(t), sinh(t))

is a numeric vector of length 2 * length(t).

The command

return(coordinates[1])

returns only the first value of this vector. (The result of coordinates[1] and cosh(t) are only identical if length(t) == 1.) To return the result of cosh(h), you could index coordinates with a sequence based on the length of t:

coordinates <- c(cosh(t), sinh(t))

return(coordinates[seq_along(t)])