不倒翁-R语言入门系列4-rep函数的用法

rep函数的官方简介：

http://127.0.0.1:15101/library/base/html/rep.html

我英语不是很好，英语好的大神自己去看官方英文说明，下面是我的简单翻译：

  Rep会重复X中的值，这是一个一般的功能，下面是详细介绍。

  rep.int and rep_len是更快的精简版，但是他们不是一般的用法。

  使用方法：

rep(x, ...)

rep.int(x, times)

rep_len(x, length.out)

参数：

X 可以是向量，列表，因子，或者日期格式（POSIXct or POSIXlt or Date object）

... ：furtherarguments to be passed to or from other methods（应该是更高级的用法，这句没看懂）下面是内在设定的参数用法：

times:重复x的次数，不能是负数和NA，应该是正整数

length.out 应该为非负整数，输出向量的期望长度，NA或者无效值将被忽略

each: 非负整数，X的每个元素将会被重复each次，如果是NA或者无效值，将会被当做1.

细节：

在缺省情况下，rep函数相当于这样的设定：

rep(x, times = 1, length.out = NA, each = 1)

通常情况下，仅仅只有一个参数会被设定，

但是如果each和其他两个钟的一个或者两个一块别设定，那么会先运行each,然后在运行其他的参数。

如果times=n是一个单个的正整数，就会重复x，进行n次。如果x=c(x1,x2,……xn),times=c(n1,n2,……nn),那么就会重复x1n1次，x2n2次，……，xn,nn次。

Length.out可能会被用于代替times，如果两个参数都存在，则会先运行length.out

Non-integer values of times will betruncated towards zero. If times is a computedquantity it is prudent to add a small fuzz or use round.And analogously for each.
If x has lengthzero and length.out is suppliedand is positive, the values are filled in using the extraction rules, that isby an NA of theappropriate class for an atomic vector (0 forraw vectors) and NULL for a list.
ValueAn object of the same type as x.
rep.int and rep_len returnno attributes (except the class if returning a factor).
The default method of rep gives theresult names (which will almost always contain duplicates) if x hadnames, but retains no other attributes.
NoteFunction rep.int is a simplecase which was provided as a separate function partly for S compatibility and partlyfor speed (especially when names can be dropped). The performance of rep hasbeen improved since, but rep.int is still atleast twice as fast when x has names.
The name rep.int long precedesmaking rep generic.
Function rep is aprimitive, but (partial) matching of argument names is performed as for normalfunctions.
For historical reasons rep (only) workson NULL: the result is always NULL evenwhen length.out is positive.
Although it has never been documented, these functions have alwaysworked on expression vectors. R 2.x.yaccepted pairlists and some other objects (although the results were rarelywhat their users intended).
ReferencesBecker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth &Brooks/Cole.
See Alsoseq, sequence, replicate.
Examplesrep(1:4, 2)rep(1:4, each = 2)       # not the same.rep(1:4, c(2,2,2,2))     # same as second.rep(1:4, c(2,1,2,1))rep(1:4, each = 2, len = 4)    # first 4 only.rep(1:4, each = 2, len = 10)   # 8 integers plus two recycled 1's.rep(1:4, each = 2, times = 3)  # length 24, 3 complete replications rep(1, 40*(1-.8)) # length 7 on most platformsrep(1, 40*(1-.8)+1e-7) # better ## replicate a listfred <- list(happy = 1:10, name = "squash")rep(fred, 5) # date-time objectsx <- .leap.seconds[1:3]rep(x, 2)rep(as.POSIXlt(x), rep(2, 3)) ## named factorx <- factor(LETTERS[1:4]); names(x) <- letters[1:4]xrep(x, 2)rep(x, each = 2)rep.int(x, 2)  # no namesrep_len(x, 10)

上面是具体用法，大家可以输入Rconsole,练习体会

另外例子中不太明白的是，

rep(1, 40*(1-.8)) # length 7 on most platforms

rep(1, 40*(1-.8)+1e-7) # better

请问大家有什么合理解释？

后面将会详细介绍sum()、max();min()

range(),mean(),median(),var(),sd(),sort(),rev(),rank(),append(),replace(),match(),pmatch(),

all(),any(),prod()等等，大约每周到每月更新一个吧。

第一个写的很烂，大家见谅。

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