lm.predictions.a1 <- predict(final.lm,clean.algae)algae <- algae[-manyNAs(algae),]clean.algae <- knnImputation(algae,k=10)clean.algaelm.a1 <- lm(a1~.,data=http://www.mamicode.com/clean.algae[,1:12])lm.a1summary(lm.a1)anova(lm.a1)lm2.a1 <- update(lm.a1,.~.-season)lm2.a1summary(lm2.a1)anova(lm.a1,lm2.a1)final.lm <- step(lm.a1)summary(final.lm)####回归树library(rpart)library(DMwR)#加载这个包，才会有海藻数据集data(algae)algae <- algae[-manyNAs(algae),]rt.a1 <- rpart(a1~.,data=http://www.mamicode.com/algae[,1:12])rt.a1prettyTree(rt.a1)printcp(rt.a1)rt2.a1 <- prune(rt.a1,cp=0.08)rt2.a1first.tree <- rpart(a1~.,data=http://www.mamicode.com/algae[,1:12])snip.rpart(first.tree,c(4,7))rt.a1 <- rpartXse(a1~.,data=http://www.mamicode.com/algae[,1:12])art.a1prettyTree(first.tree)snip.rpart(first.tree)lm.predictions.a1 <- predict(final.lm,clean.algae)summary(lm.a1)anova(lm.a1)lm2.a1 <- update(lm.a1,.~.-season)summary(lm2.a1)anova(lm.a1,lm2.a1)anova(lm2.a1)#不断重复这个过程，直到没有可剔除的候选系数final.lm <- step(lm.a1)summary(final.lm)library(rpart)data(algae)algae <- algae[-manyNAs(algae),]rt.a1 <- rpart(a1~.,data=http://www.mamicode.com/algae[,1:12])rt.a1prettyTree(rt.a1)printcp(rt.a1)rt2.a1 <- prune(rt.a1,cp=0.08)rt2.a1rt.a1 <- rpartXse(a1~.,data=http://www.mamicode.com/algae[,1:12])rt.a1first.tree <- rpart(a1~.,data=http://www.mamicode.com/algae[,1:12])snip.rpart(first.tree,c(4,7))my.tree <- snip.rpart(first.tree,c(4,7))my.treeprettyTree(first.tree)snip.rpart(first.tree)q()rt.predictions.a1 <- predict(rt.a1,algae)(mae.a1.lm <- mean(abs(lm.predictions.a1-algae[,"a1"])))(mae.a1.rt <- mean(abs(rt.predictions.a1-algae[,"a1"])))#均方误差(mse.a1.lm <- mean((lm.predictions.a1-algae[,"a1"])^2))(mse.a1.rt <- mean((rt.predictions.a1-algae[,"a1"])^2))#平均绝对误差 NMSE(nmse.a1.lm <- mean((lm.predictions.a1-algae[,‘a1‘])^2)/mean((mean(algae[,‘a1‘])-algae[,‘a1‘])^2))(nmse.a1.rt <- mean((rt.predictions.a1-algae[,‘a1‘])^2)/mean((mean(algae[,‘a1‘])-a1gae[,‘a1‘])^2))old.par <- par(mfrow=c(1,2)plot(lm.predictions.a1,clean.algae[,"a1"],main="Linear Model",xlab="Predictions",ylab="True Values")lm.predictions.a1algae[,"a1"]abline(0,1,lty=2)plot(rt.predictions.a1,clean.algae[,"a1"],main="Regression Tree",xlab="Predictions",ylab="True Values")abline(0,1,lty=2)par(old.par)algae[identify(lm.predictions.a1,clean.algae[,"a1"]),]sensible.lm.preictions.a1 <- ifelse(lm.predictions.a1<0,0,lm.predictions.a1)