R/ApproxNearest.R

In EarthSystemDiagnostics/paleospec: Spectral tools for the ECUS group

#' @title approximate a timeseries using the nearest neighbour
#' @description extends approx which always takes the right or left neighbour
#' or the weighted mean between both if f>0<1
#' @param x numeric vector giving the coordinates of the points to be interpolate
#' @param y corresponding y values
#' @param xout set of numeric values specifying where interpolation is to take place.
#' @param rule an integer (of length 1 or 2) describing how interpolation is
#' to take place outside the interval see ?approx
#' @return  a list with components 'x' and 'y', containing
#' length(xouth) coordinates which interpolate the given data points
#' @author Thomas Laepple
#' @examples
#' x<-1:10
#' y<-1:10
#' xout<-seq(from=0,to=11,by=0.01)
#' plot(x,y,type="b",pch=19,xlim=range(xout))
#' result<-ApproxNearest(x,y,xout)
#' lines(result,col="red")
#' @export
ApproxNearest <- function(x, y, xout,rule = 1)
{
    result <- list()
    result$x = xout
    result$y = approx(c(x[1], x + c(diff(x)/2, 0)), c(y[1], y),
        xout, method = "constant", f = 1,rule=rule)$y
    return(result)
}