箱线图函数：boxplot(x, ...)
## S3 method for class 'formula'
boxplot(formula, data = NULL, ..., subset, na.action = NULL)
## Default S3 method:
boxplot(x, ..., range = 1.5, width = NULL, varwidth = FALSE,        notch = FALSE, outline = TRUE, names, plot = TRUE,        border = par("fg"), col = NULL, log = "",        pars = list(boxwex = 0.8, staplewex = 0.5, outwex = 0.5),        horizontal = FALSE, add = FALSE, at = NULL)
参数说明及示例解释：1、formula:一个公式，形式为y~A（类别型变量A的每个值并列地生成数值型变量y的箱线图）或y～A*B（类别型变量A和B所有水平的两两组合生成数值型变量y的箱线图）。
代码及图形：
par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,main="car mileage data",xlab="number of cylinders", ylab="miles per gallon"）
boxplot(mpg~cyl*am,data = mtcars,main="car mileage data",xlab="number of cylinders")



2、varwidth:取值TRUE，绘制的箱线图的宽度与其样本大小的平方根成正比。
代码及图形：
par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,main="car mileage data",xlab="number of cylinders",
        ylab="miles per gallon")
boxplot(mpg~cyl,data = mtcars,varwidth=TRUE,
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")


3、width:绘制每个箱线图的相对宽度，取值向量；
par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,main="car mileage data",xlab="number of cylinders",
        ylab="miles per gallon")
boxplot(mpg~cyl,data = mtcars,width=c(1,2,3),
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")

4、notch:取值true，可绘制含凹槽的箱线图；
par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,main="car mileage data",xlab="number of cylinders",
        ylab="miles per gallon")
boxplot(mpg~cyl,data = mtcars,notch=TRUE,
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")


5、outline：默认取值TRUE,绘制离群值。如取值FALSE，不绘制离群值；
par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,notch=TRUE,
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")
boxplot(mpg~cyl,data = mtcars,notch=TRUE,outline=FALSE,
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")



6、names：每个箱线图下的组标签；
par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")
boxplot(mpg~cyl,data = mtcars,names=c(1,2,3),
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")


7、boxwex:取值向量，控制箱线图的宽度。par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")
boxplot(mpg~cyl,data = mtcars,boxwex=c(0.5,1,1.5),
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")

8、staplewex:最小值、最大值对应的钉线宽度的调整，取值向量；
par(mfrow=c(1,2))
boxplot(mpg~cyl,data = mtcars,
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")
boxplot(mpg~cyl,data = mtcars,staplewex=c(0.5,1,1.5),
        main="car mileage data",xlab="number of cylinders",ylab="miles per gallon")


9、outwex:取值向量。离群线宽度扩展，扩展比例与盒宽成正比；