linear_regression.Rmd

---
title: "Linear Regression"
author: "Zhen Huang"
date: "5/9/2020"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

---
title: Linear regression 
date: 2020-04-27 14:30:18
categories: 统计学习
tags: 统计101, R

---

> Typically, as the flexibility of f increases, its bias decreases and its variance increases 
>
> — a **bias-variance trade-off**

---

### 预处理

#### 训练/测试分割

##### 方法一

```{r}
set.seed(100)  # setting seed to reproduce results of random sampling
trainingRowIndex <- sample(1:nrow(cars), 0.8*nrow(cars))  # row indices for training data
trainingData <- cars[trainingRowIndex, ]  # model training data
testData  <- cars[-trainingRowIndex, ]   # test data
```

##### 方法二

```{r}
set.seed(1)
train=sample(c(TRUE, FALSE), nrow(cars), rep=TRUE)
test=(!train)
```

##### 方法三

```{r}
train = cars %>%
  dplyr::sample_frac(0.5)

# 相当于取了dataframe的一个否集
test = cars %>%
  setdiff(train)
```

##### 方法四



#### 数据分布情况

##### 两个变量相关性

```{r}
scatter.smooth(x=cars$speed, y=cars$dist, main="Dist ~ Speed")  # scatterplot
```



### 拟合及评估

#### `lm`

数据



###