2021-02-10

向量取值[]将TRUE对应的值取出

> x=c(7,5,3,6,1)
> x>3
[1]  TRUE  TRUE FALSE  TRUE FALSE
> x[x>3]
[1] 7 5 6
> 

> x=sample(1:100,28)
> x
 [1] 53 43 47 41 38 35 20 75 99  4 95 82  7 78 66 65 31
[18] 56 51 84 12 14 39 86 57 91  9 87
> matrix(x,nrow=7)
     [,1] [,2] [,3] [,4]
[1,]   53   75   66   14
[2,]   43   99   65   39
[3,]   47    4   31   86
[4,]   41   95   56   57
[5,]   38   82   51   91
[6,]   35    7   84    9
[7,]   20   78   12   87
> x1=sample(1:100,7);×7
```将向量进行二维排列，矩阵

x1=sample(1:100,7);x1
[1] 67 65 6 69 94 71 68
x2=11:17;x2
[1] 11 12 13 14 15 16 17
x3=sample(1:10,7);x3
[1] 9 4 2 10 8 3 5
cbind(x1,x2,x3)
x1 x2 x3
[1,] 67 11 9
[2,] 65 12 4
[3,] 6 13 2
[4,] 69 14 10
[5,] 94 15 8
[6,] 71 16 3
[7,] 68 17 5

将元素数量长度相同，数据类型相同的向量合在一个矩阵
将元素数量长度相同，数据类型不相同的向量合在一个数据框

y1=sample(1:100,7);y1
[1] 100 57 4 9 39 68 64
y2=letters[1:7];y2
[1] "a" "b" "c" "d" "e" "f" "g"
y3=sample(1:10,7);y3
[1] 3 8 5 6 4 7 9
data.frame(y1,y2,y3)
y1 y2 y3
1 100 a 3
2 57 b 8
3 4 c 5
4 9 d 6
5 39 e 4
6 68 f 7
7 64 g 9

列表：长度不同，数据类型不同，多级元素