Hi Franzi,
Up to I know you can´t predict values without you have x2,x3 and x4 parameters.
So you have three possible solution
1) set x2, x3 and x4 to Zero, *but* it will depend so much of what you want,
because if you set them to zero, it means that you are adjusting something like
mod<-lm(y~x1)
2) set x2,x3 and x4 to and mean value that you understand as rasonable for your
purpose]
and
3) build a set of for () looping, with the ranges of x2, x3 and x4, and see
what happens with the y, for each combination of x1-x2-x3-x4.
y<-runif(101)
x1<-sample(seq(0, 100))
x2<-seq(from=0,to=100,by=1)
x3<-seq(from=0,to=100,by=1)^2
x4<-exp(seq(from=0,to=100,by=1))
df<-data.frame(cbind(y,x1,x2,x3,x4))
mod<-lm(y~x1+x2+x3+x3,data=df)
df.complete<-NULL
for (x2 in seq(from=0,to=100,by=20)) {
for (x3 in seq(from=0,to=100,by=20)) {
for (x4 in seq(from=0,to=100,by=20)) {
x1<-seq(0, 100, by=10)
df.new<-data.frame(cbind(x1,x2,x3,x4))
df.new$pred<-predict(mod,new=df.new)
df.complete<-rbind(df.complete,df.new)
}}}
head(df.complete,50)
summary(df.complete)
But you have a problema. If you have four dimensions (x1-x4), it is so hard to
graph. In the case of two dimensions (like x1 and x2) you can use the function
interp() function of akima´s packge to generate a 3d plot of your response
variavel y-pred as a surface.
Good luck,
miltinho
Brazil
----- Mensagem original ----
De: Fränzi Korner <[EMAIL PROTECTED]>
Para: r-help@r-project.org
Enviadas: Terça-feira, 22 de Janeiro de 2008 11:50:03
Assunto: [R] predict from a multiple regression model
Hello
how can I predict from a lm-object over a range of values of one explanatory
variable without having to specify values for all the other explanatory
variables?
e.g.
mod<-lm(y~x1+x2+x3+x4)
x1.new<-seq(0, 100)
predict(mod, new=list(x1=x1.new))
Here, predict() does not work, since values for x2, x3 and x4 are missing.
Is there a function or argument that, in such a case, averages or weights
over the other explanatory variables, how it is done in Genstat?
Thanks
Fränzi
************************************************************************
Dr. Fränzi Korner-Nievergelt
oikostat - Statistische Analysen und Beratung
Ausserdorf 43
CH - 6218 Ettiswil
Tel.: +41 (0) 41 980 49 22
www.oikostat.ch
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Schweizerische Vogelwarte
CH - 6204 Sempach
www.vogelwarte.ch
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