看到有很多读者浏览了这篇文章，心里很是开心，为了能够更好地帮助大家，决定再修改一下，帮助大家更好地理解。
--------修改于：2018年4月28日
为了方便大家在开发环境中直接实验测试代码，下面，我将说明和函数的用法全部用英文给出（避免乱码），并加以注释，希望能够对大家有所帮助！
首先，我们来看一个seq()函数应用的实例！
x <- seq(0, 10, by = 0.01) y <- sin(x) plot(y)
下面，我们来看函数的主要使用方法！
注意：在本文调用函数时，均采用写出入口参数名的方法，比如：
seq(from = 1, to = 2)
这样函数的调用更加清晰，在调用较多函数时，不会发生混乱和参数匹配错误。
方式一：seq(from, to)
from：生成向量的起点，to：生成向量的终点，默认步长为1（可修改）
a <- seq(from = 1, to = 2) # [1, 2]
方式二：seq(from, to, by = )
by：向量元素之间的步长
a <- seq(from = 1, to = 3, by = 0.5) # [1, 1.5, 2, 2.5, 3]
方式三：seq(from, to, length.out = )
length.out：向量中元素数目
a <- seq(from = 1, to = 3, length.out = 5) # [1, 1.5, 2, 2.5, 3]
方式四：seq(along.with = )
along.with：表示生成的向量为现有一向量元素的索引
x <- c(1.2, 5.2, 6.3, 4.6) a <- seq(along.with = x) # [1, 2, 3, 4]
方式五：seq(from)
该方式和方式四功能相似
x <- c(1.2, 5.2, 6.3, 4.6) a <- seq(from = x) # [1, 2, 3, 4]
方式6：seq(length.out = )
生成从1开始，步长为1，长度为length.out的向量
a <- seq(length.out = 5) # [1, 2, 3, 4, 5]
上述几种方式为较为常见的方式，详细的函数说明如下：
Sequence Generation
Description
Generate regular sequences. seq is a standard generic with a default method. seq.int is a primitive which can be much faster but has a few restrictions. seq_along and seq_len are very fast primitives for two common cases.
---------------------------------------------
Usage
seq(...)
## 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)
seq_len(length.out)
---------------------------------------------
Arguments
1：...
arguments passed to or from methods.
2：from, to
the starting and (maximal) end values of the sequence. Of length 1 unless just from is supplied as an unnamed argument.
3：by
number: increment of the sequence.
4：length.out
desired length of the sequence. A non-negative number, which for seq and seq.int will be rounded up if fractional.
5：along.with
take the length from the length of this argument.
参考：https://blog.csdn.net/jiluben/article/details/40024607
