Convert spline interpolation to linear interpolati

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
}