[R] Use generalised additive model to plot curve

[Bill.Venables at csiro.au]

Dear Lurker,

If all you art trying to do is to plot something, isn't all you need something like the following?

x <- c( 30,  50,  80,  90, 100)
y <- c(160, 180, 250, 450, 300)
sp <- spline(x, y, n = 500)
plot(sp, type = "l", xlab = "x", ylab = "y", 
     las = 1, main = "A Spline Interpolation")
points(x, y, pch = 3, col = "red", lwd = 2) 

Bill Venables.

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of e-letter
Sent: Wednesday, 15 December 2010 8:37 AM
To: r-help at r-project.org
Subject: [R] Use generalised additive model to plot curve

Readers,

I have been reading 'the r book' by Crawley and think that the
generalised additive model is appropriate for this problem. The
package 'gam' was installed using the command (as root)

install.package("gam")
...
library(gam)

> library(gam)
Loading required package: splines
Loading required package: akima
> library(mgcv)
This is mgcv 1.3-25

Attaching package: 'mgcv'


        The following object(s) are masked from package:gam :

         gam,
         gam.control,
         gam.fit,
         plot.gam,
         predict.gam,
         s,
         summary.gam

> x<-c(30,50,80,90,100)
> y<-c(160,180,250,450,300)
> model<-gam(y~s(x))
Error in smooth.construct.tp.smooth.spec(object, data, knots) :
        A term has fewer unique covariate combinations than specified
maximum degrees of freedom

The objective is to plot y against x, finally to produce a graph with
a smooth curve (and then remove the data points). What is my mistake
please?

yours,

r251
gnu/linux mandriva2008

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