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R可视化03|ggplot2图层-几何对象图层（geom layer）
"pythonic生物人"的第101篇分享
前面简单介绍ggplot2是基于图层图形语法（the Grammar of Graphics），一张完整图由不同图层叠加而成，本文介绍几何对象图层（geom layer），续前篇：
ggplot2中geom可分为个体几何对象（Individual geoms）及群组几何对象（Collective geoms），二者区别：
1、个体几何对象（Individual geoms）
An individual geom draws a distinct graphical object for each observation (row).【一个观测值对应一个图形】
Each of these geoms is two dimensional and requires both x and y aesthetics，these geoms are the fundamental building blocks of ggplot2.
library('ggplot2')
library('gridExtra')
options(repr.plot.width = 7, repr.plot.height = 6, repr.plot.res = 250)#设置图形渲染参数
df <- data.frame(
x = c(3, 1, 5),
y = c(2, 4, 6),
label = c("a","b","c")
)
p1 <- ggplot(df, aes(x, y, label = label)) +
labs(x = NULL, y = NULL) + #隐藏坐标轴名称
theme(plot.title = element_text(size = 12))
p2 <- p + geom_point() + ggtitle("point")
p3 <- p + geom_text() + ggtitle("text")
p4 <- p + geom_bar(stat = "identity") + ggtitle("bar")
p5 <- p + geom_tile() + ggtitle("raster")
p6 <- p + geom_line() + ggtitle("line")
p7 <- p + geom_area() + ggtitle("area")
p8 <- p + geom_path() + ggtitle("path")
p9 <- p + geom_polygon() + ggtitle("polygon")
grid.arrange(p1, p2, p3, p4, p5, p6, p7, p8,p9, nrow = 4)
2、 群组几何对象（Collective geoms）
A collective geom displays multiple observations with one geometric object.【多个观测值对应一个图形】
该部分使用到数据集Oxboys, 来自 nlme package. It records the heights (height) and centered ages (age) of 26 boys (Subject), measured on nine occasions (Occasion). Subject and Occassion are stored as ordered factors.以下以几个例子帮助理解Collective geom：
#一张图展示每个Subject的身高height随年龄age变化情况
options(repr.plot.width = 7, repr.plot.height = 4, repr.plot.res = 250)#设置图形渲染参数
ggplot(Oxboys, aes(age, height, group = Subject)) + geom_point() + geom_line()#按照Subject分组绘制散点和折线图
# 不同图层不同分组
ggplot(Oxboys, aes(age, height)) +
geom_line(aes(group = Subject)) + #折线图层按照Subject分组
geom_smooth(method = "lm", size = 2, se = FALSE)#添加一个拟合线图层
ggplot(Oxboys, aes(Occasion, height)) +
geom_boxplot() +
geom_line(aes(group = Subject), colour = "#3366FF", alpha = 0.5)#设置line图层的属性，如颜色、透明度
# 个体图形属性与整体图像属性匹配
ggplot(mpg, aes(class, fill = drv)) +
geom_bar()
df <- data.frame(x = 1:3, y = 1:3, colour = c(1, 3, 5))
ggplot(df, aes(x, y, colour = factor(colour))) + geom_line(aes(group = 1), size = 2) +
geom_point(size = 5)
https://ggplot2-book.org/individual-geoms.html https://ggplot2-book.org/collective-geoms.html
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