R ggplot2 教學：基本概念與 qplot 函數

``library(ggplot2)``
``## Warning: package 'ggplot2' was built under R version 3.5.3``
``head(diamonds)``
``````## # A tibble: 6 x 10
##   carat cut       color clarity depth table price     x     y     z
##   <dbl> <ord>     <ord> <ord>   <dbl> <dbl> <int> <dbl> <dbl> <dbl>
## 1 0.23  Ideal     E     SI2      61.5    55   326  3.95  3.98  2.43
## 2 0.21  Premium   E     SI1      59.8    61   326  3.89  3.84  2.31
## 3 0.23  Good      E     VS1      56.9    65   327  4.05  4.07  2.31
## 4 0.290 Premium   I     VS2      62.4    58   334  4.2   4.23  2.63
## 5 0.31  Good      J     SI2      63.3    58   335  4.34  4.35  2.75
## 6 0.24  Very Good J     VVS2     62.8    57   336  3.94  3.96  2.48``````
``````set.seed(5)
diamonds.subset <- diamonds[sample(nrow(diamonds), 100), ]``````

ggplot繪圖文法

diamonds資料集的資料有五萬多筆

diamonds.subset <- diamonds[sample(nrow(diamonds), 100), ]

``qplot(diamonds\$carat, diamonds\$price)``

``qplot(carat, price, data = diamonds)``

``qplot(log(carat), log(price), data = diamonds)``

``qplot(carat, x * y * z, data = diamonds)``

qplot函數的運用

qplot函數是ggplot中最基本的繪圖函數

qplot 的用法是x軸與y軸的座標資料為參數(ex：qplot(diamonds\(carat, diamonds\)price))

qplot(carat, price, data = diamonds) - 使用data參數指定資料的來源

price(價格)/carat(克拉數)

log(對數) - 可透過此轉換不是線性關係的圖表

qplot(log(carat), log(price), data = diamonds)鑽石的價格與克拉數有明顯的關係

qplot(carat, x * y * z, data = diamonds) - 使用多個變數進行運算，大部分鑽石的體積都與重量成正比(密度都差不多)，也有超出的

``qplot(carat, price, data = diamonds.subset, color = color)``

``qplot(carat, price, data = diamonds.subset, shape = cut)``
``## Warning: Using shapes for an ordinal variable is not advised``

``qplot(carat, price, data = diamonds, alpha = I(1/10))``