//exam0203.txt
Name Sex Age Height Weight
Alice F 13 56.5 84.0
Becka F 13 65.3 98.0
Gail F 14 64.3 90.0
Karen F 12 56.3 77.0
Kathey F 12 59.8 84.5
Mary F 15 66.5 112.0
Sandy F 11 51.3 50.5
Sharon F 15 62.5 112.5
Tammy F 14 62.8 102.5
Alfred M 14 69.0 112.5
Duke M 14 63.5 84.0
Guido M 15 67.0 133.0
James M 12 57.3 83.0
Jeffrey M 13 62.5 84.0
John M 12 59.0 99.5
Philip M 16 72.0 150.0
Robert M 12 64.8 128.0
Thomas M 11 57.5 85.0
William M 15 66.5 112.0
由于该文件第一行是属性名称，即是含标题的.txt，所以head=TRUE。然后，编写.R脚本文件，如下：
//exam0203.R
setwd("G:\\myProject\\RDoc\\Unit1")
rt <- read.table("exam0203.txt",head=TRUE)rt
lm.sol <- lm(Weight~Height,data=rt)
summary(lm.sol)
sort（）是对向量进行从小到大的排序rank（）返回的是对向量中每个数值对应的秩
order（）返回的值表示位置，依次对应的是向量的最小值、次小值、第三小值......最大值
rank() sort() order() 和 reorder()
data<=c(2,3,6,1)
reorder()函数在ggplot2中见过：
x = reorder(Var1, -Freq) Var1是分类变量，Freq是数值型变量
help(recorder) 的结果：
Reorder Levels of a Factor
Description
reorder is a generic function. The "default" method treats its first argument as a categorical variable, and reorders its levels based on the values of a second variable, usually numeric.
Usage
reorder(x, ...)
Default S3 method:
reorder(x, X, FUN = mean, ...,
order = is.ordered(x))
