模块零：R语言快速预热

目标：熟悉 RStudio 环境，学会使用帮助文档和基础命令。

0.1 把 R 当作计算器

587 * (23234 + 899) / 9
## [1] 1574008

0.2 善用 Example 快速学习

使用 example() 函数可以直接运行包作者提供的示例代码，这是学习新函数最快的方式。

点击查看 example(boxplot) 运行结果 
  example(boxplot)
  ## 
  ## boxplt> ## boxplot on a formula:
  ## boxplt> boxplot(count ~ spray, data = InsectSprays, col = "lightgray")
  ## 
  ## boxplt> # *add* notches (somewhat funny here <--> warning "notches .. outside hinges"):
  ## boxplt> boxplot(count ~ spray, data = InsectSprays,
  ## boxplt+         notch = TRUE, add = TRUE, col = "blue")

  ## 
  ## boxplt> boxplot(decrease ~ treatment, data = OrchardSprays, col = "bisque",
  ## boxplt+         log = "y")

  ## 
  ## boxplt> ## horizontal=TRUE, switching  y <--> x :
  ## boxplt> boxplot(decrease ~ treatment, data = OrchardSprays, col = "bisque",
  ## boxplt+         log = "x", horizontal=TRUE)

  ## 
  ## boxplt> rb <- boxplot(decrease ~ treatment, data = OrchardSprays, col = "bisque")

  ## 
  ## boxplt> title("Comparing boxplot()s and non-robust mean +/- SD")
  ## 
  ## boxplt> mn.t <- tapply(OrchardSprays$decrease, OrchardSprays$treatment, mean)
  ## 
  ## boxplt> sd.t <- tapply(OrchardSprays$decrease, OrchardSprays$treatment, sd)
  ## 
  ## boxplt> xi <- 0.3 + seq(rb$n)
  ## 
  ## boxplt> points(xi, mn.t, col = "orange", pch = 18)
  ## 
  ## boxplt> arrows(xi, mn.t - sd.t, xi, mn.t + sd.t,
  ## boxplt+        code = 3, col = "pink", angle = 75, length = .1)
  ## 
  ## boxplt> ## boxplot on a matrix:
  ## boxplt> mat <- cbind(Uni05 = (1:100)/21, Norm = rnorm(100),
  ## boxplt+              `5T` = rt(100, df = 5), Gam2 = rgamma(100, shape = 2))
  ## 
  ## boxplt> boxplot(mat) # directly, calling boxplot.matrix()

  ## 
  ## boxplt> ## boxplot on a data frame:
  ## boxplt> df. <- as.data.frame(mat)
  ## 
  ## boxplt> par(las = 1) # all axis labels horizontal
  ## 
  ## boxplt> boxplot(df., main = "boxplot(*, horizontal = TRUE)", horizontal = TRUE)

  ## 
  ## boxplt> ## Using 'at = ' and adding boxplots -- example idea by Roger Bivand :
  ## boxplt> boxplot(len ~ dose, data = ToothGrowth,
  ## boxplt+         boxwex = 0.25, at = 1:3 - 0.2,
  ## boxplt+         subset = supp == "VC", col = "yellow",
  ## boxplt+         main = "Guinea Pigs' Tooth Growth",
  ## boxplt+         xlab = "Vitamin C dose mg",
  ## boxplt+         ylab = "tooth length",
  ## boxplt+         xlim = c(0.5, 3.5), ylim = c(0, 35), yaxs = "i")

  ## 
  ## boxplt> boxplot(len ~ dose, data = ToothGrowth, add = TRUE,
  ## boxplt+         boxwex = 0.25, at = 1:3 + 0.2,
  ## boxplt+         subset = supp == "OJ", col = "orange")
  ## 
  ## boxplt> legend(2, 9, c("Ascorbic acid", "Orange juice"),
  ## boxplt+        fill = c("yellow", "orange"))
  ## 
  ## boxplt> ## With less effort (slightly different) using factor *interaction*:
  ## boxplt> boxplot(len ~ dose:supp, data = ToothGrowth,
  ## boxplt+         boxwex = 0.5, col = c("orange", "yellow"),
  ## boxplt+         main = "Guinea Pigs' Tooth Growth",
  ## boxplt+         xlab = "Vitamin C dose mg", ylab = "tooth length",
  ## boxplt+         sep = ":", lex.order = TRUE, ylim = c(0, 35), yaxs = "i")