第2讲 ggplot2 数据可视化

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.title[
# 量化金融与金融编程
]
.subtitle[
## L02 ggplot2 数据可视化 | 课前预习
]
.author[
### <br>曾永艺
]
.institute[
### 厦门大学管理学院
]
.date[
### <br>2023-09-18
]

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- ## 一图胜千言

- ## The Layered Grammar of Graphics
  
- ## 将数据映射为几何对象的图形属性

- ## 统计变换、位置调整、坐标、分面

- ## 标签、标注、标度、主题等

---

### 一图胜千言

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# `ggplot2`<sup>.font60[v3.4.3]</sup> 快速入门

---
layout: true

### .bold[1 The Layered Grammar of Graphics]

---

.font130[_Data Visualization_：将.bold[数据]映射为.bold[几何对象的美学属性]]

.font110[

- 数据（.red[data]）：我们想要可视化的对象，包含变量
- 几何对象（.red[geom]etries)：用来呈现数据的几何图形对象，如点、条形、线条等
- 美学属性（.red[aes]thetic）：几何对象的视觉属性，如`x`坐标和`y`坐标位置、颜色、形状等

]

---

.font130[`ggplot2` 的语法模板]

.code150[

```r
*ggplot(data = <DATA>) +
* <GEOM_FUNCTION>(
*    mapping = aes(<MAPPINGS>),
     stat = <STAT>, 
     position = <POSITION>
  ) +
  <COORDINATE_FUNCTION> +
  <FACET_FUNCTION>
```
]

---
layout: true

### .bold[2 将.red[数据]映射为几何对象的美学属性]

---

```r
library(tidyverse)
```

```r
mpg  # print(mpg)
```

```
#> # A tibble: 234 × 11
#>   manufacturer model displ  year   cyl trans      drv     cty   hwy fl    class  
#>   <chr>        <chr> <dbl> <int> <int> <chr>      <chr> <int> <int> <chr> <chr>  
#> 1 audi         a4      1.8  1999     4 auto(l5)   f        18    29 p     compact
#> 2 audi         a4      1.8  1999     4 manual(m5) f        21    29 p     compact
#> 3 audi         a4      2    2008     4 manual(m6) f        20    31 p     compact
#> # ℹ 231 more rows
```

```r
# 查看ggplot2包内置数据集mpg的帮助文档
?mpg  # help(mpg)
```

1. `displ`: a car's engine size, in litres.
2. `hwy`: a car's fuel efficiency on the highway, in miles per gallon (mpg). 
3. `class`: "type" of car  
...

---
layout: true

### .bold[2 将数据.red[映射为几何对象的美学属性]]

---
count: false

```r
ggplot()
```

---
count: false

```r
ggplot(data = mpg)                           # 数据集
```

---
count: false

```r
ggplot(data = mpg,                           # 数据集
       mapping = aes(x = displ, y = hwy))    # 映射：变量 -> x坐标和y坐标
```

---
count: false

```r
ggplot(data = mpg,                           # 数据集
       mapping = aes(x = displ, y = hwy)) +  # 映射：变量 -> x坐标和y坐标
  geom_point()                               # 几何对象
```

---

```r
ggplot(data = mpg) + 
  geom_point(
*   mapping = aes(x = displ, y = hwy, colour = class)  # 3个映射
  )
```

---

```r
ggplot(data = mpg) + 
  geom_point(mapping = aes(x = displ, y = hwy, shape = class))
```

```
#> Warning: The shape palette can deal with a maximum of 6 discrete values because more than
#> 6 becomes difficult to discriminate; you have 7. Consider specifying shapes
#> manually if you must have them.
```

```
#> Warning: Removed 62 rows containing missing values (`geom_point()`).
```

---

.font120[
- R内置有25个形状（shape），在`ggplot2`中可用名字或数字进行设定
]
.pull-left[
<img src="L02_Visualization_Prepare_files/figure-html/shapes-name-1.png" width="95%" style="display: block; margin: auto;" />

]

.pull-right[
<img src="L02_Visualization_Prepare_files/figure-html/shapes-id-1.png" width="95%" style="display: block; margin: auto;" />

]

.font120[
- 设定图形属性相关的说明文档 .content-box-yellow.font80[`vignette("ggplot2-specs")`]
]

---

```r
ggplot(data = mpg) + 
  geom_point(
    mapping = aes(x = displ, y = hwy), 
*   shape = "triangle", size = 3, colour = "red", alpha = 0.3
    # 变量无关（“大家都一样”，即非映射）的几何对象图形属性应在aes()外进行设定
  )
```

---

```r
# layered!
ggplot(data = mpg) + 
  geom_point(mapping = aes(x = displ, y = hwy)) +
* geom_smooth(mapping = aes(x = displ, y = hwy))  # layered!
```

---

```r
ggplot(
  data = mpg,
* mapping = aes(x = displ, y = hwy)  # 共用映射，提前至ggplot()中
) +
  geom_point() +
  geom_smooth()
```

---

```r
*ggplot(mpg, aes(displ, hwy)) +       # 省略常用参数名
* geom_point(aes(colour = class)) +  # 图层自用映射
* geom_smooth(data = filter(mpg, class == "pickup"))  # 不同的数据集
```

---
layout: true

### .bold[3 .red[统计变换]、位置调整、坐标、分面]

---

```r
ggplot(data = diamonds) + 
  geom_bar(mapping = aes(x = cut))
```

.red.font110[Where comes the "count" in y-axis? 😅]

---

.font110[下面的代码会得到和使用 `geom_bar()` 相同的结果]

```r
ggplot(data = diamonds) + 
* stat_count(mapping = aes(x = cut))
```

---

```r
ggplot(data = diamonds) + 
  geom_bar(mapping = aes(x = cut, 
                         y = after_stat(prop),   # ?aes_eval
                         group = 1))             # ?aes_group_order
```

---

```r
ggplot(data = diamonds %>% group_by(cut) %>% count()) +  # 数据分组汇总计算
  geom_bar(
    mapping = aes(x = cut, y = n),
*   stat = "identity"
  )
```

---
layout: true

### .bold[3 统计变换、.red[位置调整]、坐标、分面]

---

```r
ggplot(data = diamonds) + 
  geom_bar(mapping = aes(x = cut, fill = clarity))
# geom_bar()默认的position = "stack"
```

---

```r
ggplot(data = diamonds) + 
  geom_bar(
    mapping = aes(x = cut, fill = clarity),
*   position = "dodge"  # position = position_dodge(width = 0.9)
  )
```

---

```r
ggplot(data = mpg) + 
  geom_point(
    mapping = aes(x = displ, y = hwy),
*   position = "jitter"   # same as `ggplot() + geom_jitter()`
  )
```

---
layout: true

### .bold[3 统计变换、位置调整、.red[坐标]、分面]

---

```r
ggplot(data = mpg, mapping = aes(x = class, y = hwy)) + 
  geom_boxplot() +
* coord_flip()  # ggplot2 3.3.0后直接调换x，y参数即可
```

---

```r
bar <- ggplot(data = diamonds) +  # 将图形对象存为变量bar，可在Environment标签页中检查其内容
  geom_bar(
    mapping = aes(x = cut, fill = cut), show.legend = FALSE, width = 1
  ) + 
  theme(aspect.ratio = 1) + labs(x = NULL, y = NULL)
*bar + coord_polar()
```

---
layout: true

### .bold[3 统计变换、位置调整、坐标、.red[分面]]

---

```r
ggplot(data = mpg, mapping = aes(x = displ, y = hwy)) + 
  geom_point(data = mutate(mpg, class = NULL), colour = "grey") +
  geom_point() + 
* facet_wrap(vars(class), nrow = 2) # facet_wrap(~ class, nrow = 2)
```

---

```r
ggplot(data = mpg, mapping = aes(x = displ, y = hwy)) + 
  geom_point(data = transform(mpg, cyl = NULL), colour = "grey") +
  geom_point() + 
* facet_grid(rows = vars(drv), cols = vars(cyl))  # facet_grid(drv ~ cyl)
```

---
layout: true

### .bold[4 .red[标签]、标注、标度、主题等]

---

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = class)) +
  geom_smooth(se = FALSE) +
* labs(  # 标题、小标题等
*   title = "Fuel efficiency",
*   subtitle = "... generally decreases with engine size",
*   caption = "Data from fueleconomy.gov"
* )
```

---

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = class)) +
  geom_smooth(se = FALSE) +
* labs( # 图形属性 = 标签
*   x = "Engine displacement (L)",
*   y = "Highway fuel economy (mpg)",
*   colour = "Car type"
* )
```

---
layout: true

### .bold[4 标签、.red[标注]、标度、主题等]

---

```r
# 生成辅助数据集
best <- mpg %>%
  group_by(class) %>%
  filter(row_number(desc(hwy)) == 1)
```

.pull-left[

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = class)) +
* geom_text(
    aes(label = model), 
    data = best
  )
```

]

.pull-right[

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = class)) +
* geom_label(
    aes(label = model), data = best, 
    nudge_y = 2, alpha = 0.5
  )
```

]

---

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = class)) +
* geom_point(size = 3, shape = 1, data = best) +
* ggrepel::geom_label_repel(aes(label = model), data = best)  # install ggrepel
```

---
layout: true

### .bold[4 标签、标注、.red[标度]、主题等]

---

```r
ggplot(diamonds, aes(carat, price)) +
  geom_bin2d() + 
* scale_x_log10() +
* scale_y_log10()
```

---

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point() +
* scale_y_continuous(
    name = "Highway fuel economy (mpg)",
    breaks = seq(0, 50, by = 10),
    limits = c(0, 50)
  )
```

---

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = drv, shape = drv)) +
* scale_colour_brewer(palette = "Set1")   # RColorBrewer::display.brewer.all()
```

---

```r
ggplot(mpg, aes(displ, hwy, colour = class)) +
  geom_point() +
* theme(legend.position = "bottom") +
  guides(
*   colour = guide_legend(nrow = 1, override.aes = list(size = 3))
  )
```

---
layout: true

### .bold[4 标签、标注、标度、.red[主题]等]

---

.pull-left[

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = class)) +
  geom_smooth(se = FALSE) +
* theme_minimal()
```

<img src="L02_Visualization_Prepare_files/figure-html/theme1-1.png" width="100%" style="display: block; margin: auto;" />
]

.pull-right[

```r
ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(colour = class)) +
  geom_smooth(se = FALSE) +
* ggthemes::theme_stata()   # install it!
```

<img src="L02_Visualization_Prepare_files/figure-html/theme2-1.png" width="100%" style="display: block; margin: auto;" />
]

---

.code80[

```r
theme(line, rect, text, title, aspect.ratio, axis.title, axis.title.x,
      axis.title.x.top, axis.title.x.bottom, axis.title.y, axis.title.y.left,
      axis.title.y.right, axis.text, axis.text.x, axis.text.x.top,
      axis.text.x.bottom, axis.text.y, axis.text.y.left, axis.text.y.right,
      axis.ticks, axis.ticks.x, axis.ticks.x.top, axis.ticks.x.bottom, axis.ticks.y,
      axis.ticks.y.left, axis.ticks.y.right, axis.ticks.length, axis.ticks.length.x,
      axis.ticks.length.x.top, axis.ticks.length.x.bottom, axis.ticks.length.y,
      axis.ticks.length.y.left, axis.ticks.length.y.right, axis.line, axis.line.x,
      axis.line.x.top, axis.line.x.bottom, axis.line.y, axis.line.y.left,
      axis.line.y.right, legend.background, legend.margin, legend.spacing,
      legend.spacing.x, legend.spacing.y, legend.key, legend.key.size,
      legend.key.height, legend.key.width, legend.text, legend.text.align,
      legend.title, legend.title.align, legend.position, legend.direction,
      legend.justification, legend.box, legend.box.just, legend.box.margin,
      legend.box.background, legend.box.spacing, panel.background, panel.border,
      panel.spacing, panel.spacing.x, panel.spacing.y, panel.grid, panel.grid.major,
      panel.grid.minor, panel.grid.major.x, panel.grid.major.y, panel.grid.minor.x,
      panel.grid.minor.y, panel.ontop, plot.background, plot.title,
      plot.title.position, plot.subtitle, plot.caption, plot.caption.position,
      plot.tag, plot.tag.position, plot.margin, strip.background, strip.background.x,
      strip.background.y, strip.clip, strip.placement, strip.text, strip.text.x,
      strip.text.x.bottom, strip.text.x.top, strip.text.y, strip.text.y.left,
      strip.text.y.right, strip.switch.pad.grid, strip.switch.pad.wrap, ...,
      complete = FALSE, validate = TRUE)
```
]

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