library(corrplot)
png("C:/temp/corrbmw.png",width=300,height=1500)
par(mfrow=c(2,3))
for(mod in sort(unique(bmw$model))){
  tbmw = subset(bmw,model==mod)
  corbmw <- tbmw[,sapply(tbmw,is.numeric) & sapply(tbmw,function(inv){sd(inv,na.rm=T)>0})]
  corrplot(cor(corbmw,use="pairw"),main=mod,mar=c(0,0,1,0))  
}
dev.off()