R读书笔记一：变量，向量，数组，矩阵，数据框，读写文件，控制流

R读书笔记一：变量，向量，数组，矩阵，数据框，读写文件，控制流

1、创建向量和矩阵

函数c( ), length( ), mode( ), rbind( ), cbind( )

1）创建向量，求向量长度，向量类型。

> x1=c(2,4,6,8,0)

> x2=c(1,3,5,7,9)

> length(x1)

[1] 5

> mode(x1)

[1] "numeric"

> x1

[1] 2 4 6 8 0

> x1[3]

[1] 6

> a1=c(1:100)

> length(a1)

[1] 100

2）创建矩阵，向量合成矩阵。

> rbind(x1,x2)

   [,1] [,2] [,3] [,4] [,5]

x1    2    4    6    8    0

x2    1    3    5    7    9

> cbind(x1,x2)

     x1 x2

[1,]  2  1

[2,]  4  3

[3,]  6  5

[4,]  8  7

[5,]  0  9

> m1=rbind(x1,x2)

> m1

   [,1] [,2] [,3] [,4] [,5]

x1    2    4    6    8    0

x2    1    3    5    7    9

2、求平均值，和，连乘，最值，方差，标准差

函数mean( ), sum( ), min( ), max( ), var( ), sd( ), prod( )

> x=c(1:100)

> mean(x)

[1] 50.5

> sum(x)

[1] 5050

> max(x)

[1] 100

> min(x)

[1] 1

> var(X)

错误于is.data.frame(x) : 找不到对象‘X‘

> var(x)

[1] 841.6667

> prod(x)

[1] 9.332622e+157

> sd(x)

[1] 29.01149

3、寻求帮助

> help(matrix)

> help(mode)

4、一些函数

1）which( )函数

> a=c(2,3,4,2,5,1,6,3,2,5,8,5,7,3)

> which.max(a)

[1] 11

> which.min(a)

[1] 6

> a[which.max(a)]

[1] 8

> which(a==2)

[1] 1 4 9

> a[which(a==2)]

[1] 2 2 2

> which(a>5)

[1]  7 11 13

> a[which(a>5)]

[1] 6 8 7

2）seq( )函数

> seq(5,20)

 [1]  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20

> seq(5,121,by=2)

 [1]   5   7   9  11  13  15  17  19  21  23  25  27  29  31  33  35  37  39  41  43  45  47

[23]  49  51  53  55  57  59  61  63  65  67  69  71  73  75  77  79  81  83  85  87  89  91

[45]  93  95  97  99 101 103 105 107 109 111 113 115 117 119 121

> seq(5,121,by=2,length=10)

错误于seq.default(5, 121, by = 2, length = 10) : 太多参数

> seq(5,121,length=10)

 [1]   5.00000  17.88889  30.77778  43.66667  56.55556  69.44444  82.33333  95.22222

 [9] 108.11111 121.00000

3）字母序列letters

> letters[1:30]

 [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s" "t" "u" "v"

[23] "w" "x" "y" "z" NA  NA  NA  NA 

5、生成矩阵

> a1=c(1:12)

> matrix(a1,nrow=3,ncol=4)

     [,1] [,2] [,3] [,4]

[1,]    1    4    7   10

[2,]    2    5    8   11

[3,]    3    6    9   12

> matrix(a1,nrow=4,ncol=3)

     [,1] [,2] [,3]

[1,]    1    5    9

[2,]    2    6   10

[3,]    3    7   11

[4,]    4    8   12

> matrix(a1,nrow=4,ncol=3,byrow=T)

     [,1] [,2] [,3]

[1,]    1    2    3

[2,]    4    5    6

[3,]    7    8    9

[4,]   10   11   12

6、数据框

> x1=c(10,13,45,26,23,12,24,78,23,43,31,56)

> x2=c(20,65,32,32,27,87,60,13,42,51,77,35)

> x=data.frame(x1,x2)

> x

   x1 x2

1  10 20

2  13 65

3  45 32

4  26 32

5  23 27

6  12 87

7  24 60

8  78 13

9  23 42

10 43 51

11 31 77

12 56 35

> x=data.frame(‘重量‘=x1,‘运费‘=x2)

> x

   重量 运费

1    10   20

2    13   65

3    45   32

4    26   32

5    23   27

6    12   87

7    24   60

8    78   13

9    23   42

10   43   51

11   31   77

12   56   35