[R] Predictions with GAM

[Gavin Simpson]

On Fri, 2009-01-16 at 12:36 +0100, Robbert Langenberg wrote:
> Dear,
> 
> I am trying to get a prediction of my GAM on a response type. So that I
> eventually get plots with the correct values on my ylab.
> I have been able to get some of my GAM's working with the example shown
> below:
> *
> model1<-gam(nsdall ~ s(jdaylitr2), data=datansd)
> newd1 <- data.frame(jdaylitr2=(244:304))
> pred1 <- predict.gam(model1,newd1,type="response")*

Hi Robert,

You want predictions for the covariate over range 244:304 for each of
your 8 mapID's, yes?

This is not tested, but why not something like:

newd2 <- data.frame(jdaylitr2 = rep(seq(244, 304, length = 100), 8),
                    mapID = rep(levels(datansd$mapID), each = 100))

Then use newd2 in your call to predict.

I am assuming that datansd$mapID is a factor in the above. If it is just
some other indicator variable, then perhaps something like:

newd2 <- data.frame(jdaylitr2 = rep(seq(244, 304, length = 100), 8),
                    mapID = rep(sort(unique(datansd$mapID)), 
                                each = 100))

Does that work for you?

HTH

G

> 
> The problem I am encountering now is that I cannot seem to get it done for
> the following type of model:
> 
> *model3<-gam(y_no~s(day,by=mapID),family=binomial, data=mergeday)*
> 
> My mapID consists of 8 levels of which I get individual plots with *
> plot(model3)*. When I do predict with a newdata in it just like my first
> model I need all columns to have the same amount of rows or else R will not
> except it ofcourse, the col.names need to at least include day and mapID.
> This way I can not get a prediction working for this GAM, I am confused
> because of this part in the model: *s(day,by=mapID).
> 
> *I have been reading through the GAM, an introduction with R book from Wood,
> S. but could not find anything about predictions with BY in the model.
> 
> I hope someone can help me out with this,
> 
> Sincerely yours,
> 
> Robbert Langenberg
> 
> 	[[alternative HTML version deleted]]
> 
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