R语言基础Lecture6

因子（Factor）

> factor = factor(rep(c(1:3),time=5))#1到3循环5次
> factor
 [1] 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3
Levels: 1 2 3
> X=sample(100,15)#从1~100中抽取15个
> tapply(X,factor,mean)#求level等于1、2、3的平均值
   1    2    3 
67.6 52.2 56.8 
> rbind(X,factor)
       [,1] [,2] [,3] [,4] [,5] [,6] [,7]
X        97   87   93   34   16   67   48
factor    1    2    3    1    2    3    1
       [,8] [,9] [,10] [,11] [,12] [,13]
X        43   25    77    21    60    82
factor    2    3     1     2     3     1
       [,14] [,15]
X         94    39
factor     2     3
#验证
> rbind(X,factor)[2,]==1#取出X中factor为1的数
 [1]  TRUE FALSE FALSE  TRUE FALSE FALSE
 [7]  TRUE FALSE FALSE  TRUE FALSE FALSE
[13]  TRUE FALSE FALSE
> boo = rbind(X,factor)[2,]==1#作为判断条件
> which(boo)#返回True的数的下标
[1]  1  4  7 10 13
> rbind(X,factor)[1,which(boo)]#取出下标对应的值
[1] 97 34 48 77 82
> sum(rbind(X,factor)[1,which(boo)])/length(which(boo))#求平均值
[1] 67.6