> seq(from=10,to=20,by=3)
[1] 10 13 16 19
> seq(from=10,to=20,length=5)
[1] 10.0 12.5 15.0 17.5 20.0
## Default S3 method:
seq(from = 1, to = 1, by = ((to - from)/(length.out - 1)),
length.out = NULL, along.with = NULL, ...)
seq.int(from, to, by, length.out, along.with, ...)
seq_along(along.with) 从这个参数的长度取长度
seq_len(length.out) 序列所需长度
> data.frame(a=seq_along(mtcars$mpg),b=mtcars$mpg,c=seq(along.with= mtcars$mpg))
a b c
1 21.0 1
2 21.0 2
3 22.8 3
4 21.4 4
5 18.7 5
6 18.1 6
7 14.3 7
8 24.4 8
9 22.8 9
10 19.2 10
11 17.8 11
12 16.4 12
13 17.3 13
14 15.2 14
15 10.4 15
16 10.4 16
17 14.7 17
18 32.4 18
19 30.4 19
20 33.9 20
21 21.5 21
22 15.5 22
23 15.2 23
24 13.3 24
25 19.2 25
26 27.3 26
27 26.0 27
28 30.4 28
29 15.8 29
30 19.7 30
31 15.0 31
32 21.4 32
原文：http://www.cnblogs.com/wwxbi/p/6087350.html