loessDemo function

Graphical Interactive Demo of loess()

A graphical and interactive demonstration and visualization of how loess works. By clicking on the graphic, the user determines the current estimation window which is visualized together with the weights.

loessDemo(x, y, span = 1/2, degree = 1, family = c("gaussian", "symmetric"),
          nearest = FALSE, nout = 501,
          xlim = numeric(0), ylim = numeric(0), strictlim = TRUE, verbose = TRUE,
          inch.sym = 0.25, pch = 4, shade = TRUE, w.symbols = TRUE,
          sym.col = "blue", w.col = "light blue", line.col = "steelblue")

Arguments

• x,y: numeric vectors of the same length; the demo is about loess(y ~ x).

• span: the smoothing parameter $\alpha$.

• degree: the degree of the polynomials to be used; must be in ${0,1,2}$.

• family: if "gaussian" fitting is by least-squares, and if "symmetric" a re-descending M estimator is used with Tukey's biweight function. Can be abbreviated.

• nearest: logical indicating how $x_0$ should be determined, the value at which $f^(x_0)$ is computed. If nearest is true, the closest data value is taken.

• nout: the number of points at which to evaluate, i.e, determining $u_i$, $i = 1,2, \dots, \mathtt{nout}$, at which $f^(u_i)$ is computed.

• xlim: x-range; to extend or determine (iff strictlim is true) the $x$-range for plotting.

• ylim: y-range; to extend or determine (iff strictlim is true) the $y$-range for plotting.

• strictlim: logical determining if xlim and ylim

  should be strict limits (as e.g., in plot.default), or just a suggestion to extend the data-dependent ranges.

• verbose: logical ......

• inch.sym: symbol size in inches of the maximal weight circle symbol.

• pch: plotting character, see points.

• shade: logical; if true, polygon(.., density=..)

  will be used to shade off the regions where the weights are zero.

• w.symbols: logical indicating if the non-zero weights should be visualized by circles with radius proportional to inch.sym

  and $\sqrt{w}$ where $w$ are the weights.

• sym.col, w.col, line.col: colors for the symbols, weights and lines, respectively.

Author(s)

As function loess.demo(), written and posted to S-news, on 27 Sep 2001, by Greg Snow, Brigham Young University,

it was modified by Henrik Aa. Nielsen, IMM, DTU,

and subsequently spiffed up for by Martin Maechler.

See Also

loess.

Examples

if(dev.interactive()) {

 if(requireNamespace("lattice")) {
    data("ethanol", package = "lattice")
    attach(ethanol)
    loessDemo(E,NOx, span=.25)
    loessDemo(E,NOx, span=.25, family = "symmetric")

    loessDemo(E,NOx, degree=0)# Tricube Kernel estimate
  }

 ## Artificial Example with one outlier
 n2 <- 50; x <- 1:(1+2*n2)
 fx <- (x/10 - 5)^2
 y <- fx + 4*rnorm(x)
 y[n2+1] <- 1e4
 loessDemo(x,y, span=1/3, ylim= c(0,1000))# not robust !!
 loessDemo(x,y, span=1/3, family = "symm")
 loessDemo(x,y, span=1/3, family = "symm", w.symb = FALSE, ylim = c(0,40))
 loessDemo(x,y, span=1/3, family = "symm", ylim = c(0,40))
 ## but see warnings() --- there's a "fixup"

}