R语言可视化及作图10--ggplot2的theme函数

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R语言绘图系列：

• R语言可视化及作图1--基础绘图（par函数，散点图，盒形图，条形图，直方图）
• R语言可视化及作图2--低级绘图函数
• R语言可视化及作图3--图形颜色选取
• R语言可视化及作图4--qplot和ggplot2美学函数
• R语言可视化及作图5--ggplot2基本要素和几何对象汇总
• R语言可视化及作图6--ggplot2之点图、条形图、盒形图、直方图、线图
• R语言可视化及作图7--ggplot2之标签、图例和标题绘制
• R语言可视化及作图8--坐标轴自定义和坐标系转换
• R语言可视化及作图9--主题函数

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theme函数主要的用途是调节图的主题。如下图，主题主要分为整幅图plot，坐标轴axis，图例legend，面板panel和分面元素facet。其中经常用到的是坐标轴主题的修改，比如常见的坐标轴字体大小的修改。

theme函数其实很简单:
theme(主题.部件=element_类型())
主题：plot, axis, legend, panel, facet
部件：title(名字，坐标轴名字), line(线，坐标轴的xy轴), text(标签，坐标轴刻度的数字), ticks(坐标轴刻度的小线条), background(背景)等
类型：rect(所有矩形区域属性)，line(所有线属性)，text(所有文本相关属性)，title(所有标题属性)
说明：部件要和类型一致。比如，部件为title，text等文字相关的元素，那么类型处就为text (具体见上图)。

1. 整幅图的主题设置Plot elements

library(tidyverse)
head(mtcars)
p1=ggplot(mtcars,aes(mpg,disp))+geom_point()

p1+labs(title="xyz")+theme(
    plot.background = element_rect(fill = "lightblue", color = "pink", size = 15),
    plot.title = element_text(hjust = 1, color = "black", face = "bold",size=15),
    plot.margin = margin(t = 30, r = 30, b = 30, l = 30, unit = "pt"))

2. 坐标轴主题设置Axis elements

p1+theme(
    axis.line = element_line(color = "lightblue", size = 1),
    axis.title = element_text(color = "black", face = "italic"),
    axis.ticks = element_line(color = "purple", size = 2),
    axis.text = element_text(color = "lightpink"),
    axis.text.x = element_text(angle = 45, hjust = 1)
)

3. 面板元素设置

p1+ theme(
    panel.background = element_rect(fill = "white", color = "purple"),
    panel.grid = element_line(color = "grey80", size = 0.3)
)

4. 图例设置

p2=ggplot(mtcars,aes(mpg,disp,color=cyl))+geom_point()
p2+theme(
    legend.background = element_rect(fill = "lightgrey"),
    legend.title = element_text(color = "black", size = 15),
    legend.key = element_rect(fill = "black"),
    legend.text = element_text(color = "blue"),
    legend.margin = margin(t = 20, r = 10, b = 10, l = 10, unit = "pt"),
    legend.position = "right"
)

5. 参考ggplot2预设主题，绘制自己的theme

ggplot2的预设主题已经写过了，参考R语言可视化及作图9--主题函数。
以theme_linedraw()为例，查看这个主题设置了什么参数

theme_linedraw
## function (base_size = 11, base_family = "", base_line_size = base_size/22, 
##     base_rect_size = base_size/22) 
## {
##     half_line <- base_size/2
##     theme_bw(base_size = base_size, base_family = base_family, 
##         base_line_size = base_line_size, base_rect_size = base_rect_size) %+replace% 
##         theme(axis.text = element_text(colour = "black", size = rel(0.8)), 
##             axis.ticks = element_line(colour = "black", size = rel(0.5)), 
##             panel.border = element_rect(fill = NA, colour = "black", 
##                 size = rel(1)), panel.grid = element_line(colour = "black"), 
##             panel.grid.major = element_line(size = rel(0.1)), 
##             panel.grid.minor = element_line(size = rel(0.05)), 
##             strip.background = element_rect(fill = "black"), 
##             strip.text = element_text(colour = "white", size = rel(0.8), 
##                 margin = margin(0.8 * half_line, 0.8 * half_line, 
##                   0.8 * half_line, 0.8 * half_line)), complete = TRUE)
## }
## <bytecode: 0x7f818ba6d600>
## <environment: namespace:ggplot2>

它无非是一个具有两个参数的函数：base_size和base_family。其主题部分直接应用的theme函数就是前面写的主题设置函数，这一部分可以直接使用前面介绍的参数进行修改。