My notes for R programming

Based on electronic version of R for data science

20200206-20200207 chapter1- chapter3- Data visualization

#This blog  mainly focuses on chapter 3 -Data visualization

library(ggplot2)  #使用前先载入包

#h绘图模板如下：
ggplot(data = <DATA>) +
  <GEOM_FUNCTION>(mapping = aes(<MAPPINGS>))

#ggplot2有很多geom函数，如geom_smooth,geom_point,geom_boxplot等，每个geom函数都有一个mapping参数，定义变量的mapping方式
#mapping 和aes()通常一起出现， aes里是绘图参数，不同的geom函数包含的aes参数不完全一样，共有x=varible_name,y=,cologgr等；但smooth里有linetype = variable_name，group = variable_name, 而point里没有。
#> Warning: Using size for a discrete variable is not advised.
ggplot(data = mpg) +
  geom_point(mapping = aes(x = displ, y = hwy, color = trans)) #或者自定义颜色geom_point(mapping = aes（...), color = "blue")
ggplot(data = mpg) +
  geom_point(mapping = aes(x = displ, y = hwy)) +
  facet_wrap(. ~ class) #两个变量时可以用facet_wrap也可以用facet_grid,区别是前者变量同轴排列，后者异轴排列（网格数量为x*y个，不能设置nrow和ncol）。
#用 . 代替x/y轴的变量，则所在轴只有一行/列

coord_flip() #转换横纵坐标系

ggplot(data = mpg, mapping = aes(x = cty, y = hwy)) + #全局设置，还可以设置color等共有的aes参数
       geom_point() + #该图层接受全局设置，无单独设置；
       geom_abline(size = 2, color = "orange") + #该图层单独设置；括号里不能写mapping = aes（size = ...),而是这样写！！！！
       coord_fixed()

> ggplot(data = mpg, mapping = aes(displ,hwy))+
    geom_point(color = drv)+ #没加mapping=aes不能设置（？？？），下同
    geom_smooth(se = FALSE , size = 2, group = drv)
#Error in layer(data = data, mapping = mapping, stat = stat, geom = GeomPoint,  : 找不到对象'drv'

> ggplot(data = mpg, mapping = aes(displ,hwy))+
    geom_point(mapping = aes(color = drv))+
    geom_smooth(mapping = aes(size = 2, group = drv),se = FALSE)
#geom_smooth()` using method = 'loess' and formula 'y ~ x'

#template
ggplot(data = <DATA>) +
  <GEOM_FUNCTION>(
    mapping = aes(<MAPPINGS>),
    stat = <STAT>,
    position = <POSITION>
  ) +
  <COORDINATE_FUNCTION> +
  <FACET_FUNCTION>
 
#The grammar of graphics is based on the insight that you can uniquely describe any plot as a combination of a dataset, a geom, a set of mappings, a stat, a position adjustment, a coordinate system, and a faceting scheme.