Convert spline interpolation to linear interpolation?

Question

This function below is doing good job for spline interpolation but I wonder how can I modify it to do linear interpolation instead!

  ## Function to interpolate using spline
    imageSpline = function(x, y, xout, method = "natural", ...){
    x.max = max(xout)
    x.spline = spline(x = x, y = y, xout = xout, method = method, ...)
    x.spline
    }

Answer 1

See ?approx for approx() and approxFun() . These are the linear interpolation counterparts to spline() and splineFun() .

Depending on the detail of the linear interpolation you want to perform (see ?approx for the details and things to tweak), it could be as simple as:

imageApprox <- function(x, y, xout, ...) {
    x.linear <- approx(x = x, y = y, xout = xout, ...)
    x.linear
}