[R] Odp: Understanding how R works

[Petr PIKAL]

Hi

r-help-bounces at r-project.org napsal dne 28.07.2010 10:08:37:

> Hello everyone.
> I am more than new into R.
> Today I have started reading about  grf function that is included in 
geoR 
> package. 
> 
> According the manual (vignette?)
> 
> 
> grf() generates (unconditional) simulations of Gaussian random fields 
for given 
> covariance parameters. geoR2RF converts model specification used by geoR 
to the 
> correponding one in RandomFields.
> 
> I would like to use this function to fill in with valies a rasterlayer.
> 
> According to the manual grf() returns a list
> 
> Value
> grf returns a list with the components: 
> coords   an n x 2 matrix with the coordinates of the simulated data. 
>   data   a vector (if nsim = 1) or a matrix with the simulated values. 
For the 
> latter each column corresponds to one simulation. 
> 
>   cov.model   a string with the name of the correlation function. 
>   nugget   the value of the nugget parameter.
>   cov.pars   a vector with the values of sigma^2 and phi, respectively. 
>   kappa   value of the parameter kappa. 
>   lambda   value of the Box-Cox transformation parameter lambda. 
>   aniso.pars   a vector with values of the anisotropy parameters, if 
provided in 
> the function call. 
> 
>   method   a string with the name of the simulation method used.
>   sim.dim   a string "1d" or "2d" indicating the spatial dimension of 
the 
> simulation.
>   .Random.seed   the random seed by the time the function was called. 
>   messages   messages produced by the function describing the 
simulation. 
>   call   the function call. 
>   geoR2grf returns a list with the components: 
> model  RandomFields name of the correlation model
>   param  RandomFields parameter vector
> 
> 
> And this is exactly the point I do not get.
> In the example section of the same function I can find the following:
> 
> sim1 <- grf(100, cov.pars = c(1, .25))
> # a display of simulated locations and values
> points(sim1)
> 
> How the function points() understand what to read exactly from the list?

You can track R functions sometimes by typing name of function or look if 
there are methods for some object
e.g.

> methods(points)
[1] points.default  points.formula* points.table* 

   Non-visible functions are asterisked
> points.default
function (x, y = NULL, type = "p", ...) 
plot.xy(xy.coords(x, y), type = type, ...)
<environment: namespace:graphics>

> xy.coords
function (x, y = NULL, xlab = NULL, ylab = NULL, log = NULL, 
    recycle = FALSE) 
{
    if (is.null(y)) {
        ylab <- xlab
        if (is.language(x)) {
            if (inherits(x, "formula") && length(x) == 3) {
                ylab <- deparse(x[[2L]])
                xlab <- deparse(x[[3L]])
                y <- eval(x[[2L]], environment(x), parent.frame())
                x <- eval(x[[3L]], environment(x), parent.frame())
            }
            else stop("invalid first argument")
        }
        else if (inherits(x, "ts")) {
            y <- if (is.matrix(x)) 
                x[, 1]
            else x
            x <- stats::time(x)
            xlab <- "Time"
        }
        else if (is.complex(x)) {
            y <- Im(x)
            x <- Re(x)
            xlab <- paste("Re(", ylab, ")", sep = "")
            ylab <- paste("Im(", ylab, ")", sep = "")
        }

....

So you could check if there is points method for grf object

Regards
Petr

> 
> I would like tot hank you in advance for your replies
> Best Regards
> Alex
> 
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