HW1-trees-sol.Rmd

---
title: "Week3-HW-Trees"
author: "Brian Quistorff"
date: "June 26, 2017"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
setwd("C:/Users/bquist/OneDrive - Microsoft/DS3")
library(rpart)
library(rpart.plot)
library(glmnet)
```

## R Markdown


```{r part1}
df = data.frame(x = 1:100)
df$e = rnorm(100)
df$y = df$x + df$e
tree = rpart(y~x,data=df)
rpart.plot(tree)
```

```{r part1a}
df$x2 = df$x*df$x
df$y2 = df$x2 + df$e
tree2 = rpart(y2~x,data=df)
rpart.plot(tree2)
```

```{r part2}
df$xcut = ifelse(df$x>50, 1, 0)
df$y3 = 2 * df$xcut + df$e

tree3 = rpart(y3~x,data=df)
rpart.plot(tree3)
df$y3_tree_pred = predict(tree3, data=df)
df$y3_tree_sqerr = (df$y3-df$y3_tree_pred)^2
mean(df$y3_tree_sqerr)

df$x3 = df$x^3
x_lasso = as.matrix(df[,c("x", "x2", "x3")])
y3 = as.vector(df$y3)
lasso3 = cv.glmnet(x_lasso, y=y3, alpha=1)
df$y3_lasso_pred = predict(lasso3, newx=x_lasso)
df$y3_lasso_sqerr = (df$y3-df$y3_lasso_pred)^2
mean(df$y3_lasso_sqerr)
```