解普通方程组可以用函数solve(),solve()的基本用法是solve(A,b),其中,A为方程组的系数矩阵,b为方程组的右端。例如:已知方程组 :2x1+2x3=1;2x1+x2+2x3=2;2x1+x2=3。
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))