p_Section 20 (additive model)

# install.packages( c("mgcv", "spData") )
library(mgcv)
library(spData)

#### Lucas housing price data
data(house)
dat<-as.data.frame(house)
dat[1:4,]

##### Additive model
formula    <- log(price) ~ s(TLA) + s(yrbuilt) + garagesqft + s(wall, bs="re")
mod  	     <- gam(formula, data = dat)
summary(mod)
plot(mod,select=1)
plot(mod,select=2)

coefs       <-coefficients(mod)	
wall_id     <-grep("wall",names(coefs))
coefs_wall  <-coefs[wall_id]
coefs_wall2 <-data.frame(wall=levels(dat$wall),coefs=coefs_wall)
coefs_wall2