R是用于统计分析、绘图的语言和操作环境。R是属于GNU系统的一个自由、免费、源代码开放的软件，它是一个用于统计计算和统计制图的优秀工具。它是一套由数据操作、计算和图形展示功能整合而成的套件。包括：有效的数据存储和处理功能，一套完整的数组（特别是矩阵）计算操作符，拥有完整体系的数据分析工具，为数据分析和显示提供的强大图形功能，一套（源自S语言）完善、简单、有效的编程语言（包括条件、循环、自定义函数、输入输出功能）。
如何用RStudio做分位数图呢？
#分位数图，画t分布密度带p值x=seq(-6,6,length=1000);y=dt(x,19)r1=-6;r2=-2.89;x2=c(r1,r1,x[x<r2&x>r1],r2,r2)y2=c(0,dt(c(r1,x[x<r2&x>r1],r2),19),0)plot(x,y,type="l",ylab="Density oft(19)",xlim=c(-5,5))abline(h=0);polygon(x2,y2,col="red")title("Tail Probability for t(19)")text(c(-4.1,-2,5),c(0.02,-0.07),c("p-value=0.0047","t=-2.89"))#对称#x=seq(-6,6,length=1000);y=dt(x,19)r1=6;r2=2.89;x2=c(r1,r1,x[x<r2&x>r1],r2,r2)y2=c(0,dt(c(r1,x[x<r2&x>r1],r2),19),0)plot(x,y,type="l",ylab="Density oft(19)",xlim=c(-5,5))abline(h=0);polygon(x2,y2,col="red")title("Tail Probability for t(19)")text(c(-4.1,-2,5),c(0.02,-0.07),c("p-value=0.0047","t=-2.89"))#两边#x=seq(-6,6,length=1000);y=dt(x,19)r1=-6;r2=-2.89;r3=2.89;r4=6;x2=c(r1,r1,x[x<r2&x>r1],r2,r2)y2=c(0,dt(c(r1,x[x<r2&x>r1],r2),19),0)x3=c(r3,r3,x[x<r4&x>r3],r4,r4)y3=c(0,dt(c(r3,x[x<r4&x>r3],r4),19),0)plot(x,y,type="l",ylab="Density oft(19)",xlim=c(-5,5))abline(h=0);polygon(c(x2,x3),c(y2,y3),col="red");title("Tail Probability for t(19)")text(c(-4.1,-2.5),c(0.02,-0.007),c("p-value=0.0047","t=-2.89"))text(c(2.5,4.1),c(0.02,-0.007),c("p-value=0.9953","t=2.89"))#正态分布x=seq(-5,5,0.01)#得到步长0.01的x范围plot(x,dnorm(x),type="l",xlim=c(-5,5),ylim=c(0,2),main="The Normal Density Distribution") #画curve(dnorm(x,1,0.5),add=T,lty=2,col="blue")lines(x,dnorm(x,0,0.25),col="green")lines(x,dnorm(x,-2,0.5),col="orange")legend("topright",legend=paste("m=",c(0,1,0,-2),"sd=", #m:均值 sd:方差c(1,0.5,0.25,0.5)),lwd=3,lty=c(1,2,1,1),col=c("black","blue","green","red"))#分布函数set.seed(1)X<-seq(-5,5,length.out=100)y<-pnorm(x,0,1)plot(x,y,col="red",xlim=c(-5,5),ylim=c(0,1),type="l",xaxs="i",yaxs="i",ylab='density',xlab='',main="The Normal Cumulative Distribution")lines(x,pnorm(x,0,0.5),col="green")lines(x,pnorm(x,0,2),col="blue")lines(x,pnorm(x,-2,1),col="orange")legend("bottomright",legend=paste("m=",c(0,0,0,-2),"sd=",c(1,0.5,2,1)),lwd=1,col=c("red","green","blue","orange"))
得到的图形结果如下：
