How to map a vector to a different range in R?

Question

I have a vector in the range [1,10]

c(1,2,9,10)

and I want to map it to a different range, for example [12,102]

Answer 1

linMap <- function(x, from, to)
  (x - min(x)) / max(x - min(x)) * (to - from) + from

linMap(vec, 12, 102)
# [1]  12  22  92 102

Or more explicitly:

linMap <- function(x, from, to) {
  # Shifting the vector so that min(x) == 0
  x <- x - min(x)
  # Scaling to the range of [0, 1]
  x <- x / max(x)
  # Scaling to the needed amplitude
  x <- x * (to - from)
  # Shifting to the needed level
  x + from
}

rescale(vec, c(12, 102)) works using the package scales. Also one could exploit approxfun in a clever way as suggested by @flodel:

linMap <- function(x, a, b) approxfun(range(x), c(a, b))(x)