1.向量类似于数学中的集合概念

2.用函数c来创建向量

> x <- c(1,2,3,4,5)
> y <- c("apple","pineapple","banana")
> z <- c(TRUE,T,F)
> M <- c(1:100)
> N <- seq(from=1,to=100,by=2)
> L <- seq(from=1,to=100,length.out=5)
> ?rep
> rep(2,5)
[1] 2 2 2 2 2
> rep(2,5)
[1] 2 2 2 2 2
> rep(x,5)[1] 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
> rep(x,each=5)[1] 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5
> rep(x,each=5,times=2)[1] 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 5 5 5 5 5 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3
[41] 4 4 4 4 4 5 5 5 5 5

3.向量索引

（1）正负整数索引

    R的索引是从1开始，而不是从0。其次，R的负数索引不代表逆序索引，而是表示除该绝对值不引用外的其他所有值。

> x <- c(1:100)
> length(x)
[1] 100
> x[1]
[1] 1
> x[0]
integer(0)
> x[-19][1]   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15  16  17  18  20  21
[21]  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41
[41]  42  43  44  45  46  47  48  49  50  51  52  53  54  55  56  57  58  59  60  61
[61]  62  63  64  65  66  67  68  69  70  71  72  73  74  75  76  77  78  79  80  81
[81]  82  83  84  85  86  87  88  89  90  91  92  93  94  95  96  97  98  99 100
> x[c(4:20)][1]  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
> x[c(1,3,15,34,23)]
[1]  1  3 15 34 23
> x[c(-2,3,4)]
Error in x[c(-2, 3, 4)] : only 0's may be mixed with negative subscripts

（2）逻辑向量索引

只输出逻辑值为真的数值

> y <- c(1:10)
> y[1]  1  2  3  4  5  6  7  8  9 10
> y[c(T,T,F,T,T,F,F,F,T,F)]
[1] 1 2 4 5 9
> y[c(T)][1]  1  2  3  4  5  6  7  8  9 10
> y[c(F)]
integer(0)
> y[c(T,F)]
[1] 1 3 5 7 9
> y[c(T,T,F,T,T,F,F,F)]
[1]  1  2  4  5  9 10
> y[c(T,T,F,T,T,F,F,F,T,F,T,F)]
[1]  1  2  4  5  9 NA
> y[y>5]
[1]  6  7  8  9 10
> y[y>5 & y<9]
[1] 6 7 8

> z <- c("one","two","three","four","five")
> z
[1] "one"   "two"   "three" "four"  "five" 
> z[ "one" %in% z]
[1] "one"   "two"   "three" "four"  "five" 
> z[z %in% c("one","two")]
[1] "one" "two"
> z %in% c("one","two")
[1]  TRUE  TRUE FALSE FALSE FALSE
> k <- z %in% c("one","two")
> z[k]
[1] "one" "two"

 

（3）名称索引

> names(y)
NULL
> names(y) <- c("one","two","three","four","five","six","seven")
> yone   two three  four  five   six seven  <NA>  <NA>  <NA> 1     2     3     4     5     6     7     8     9    10 
> names(y)[1] "one"   "two"   "three" "four"  "five"  "six"   "seven" NA      NA      NA     
> y["one"]
one 1 
> y[1]
one 1