R中rep函數的使用

官方幫助文檔如下寫的：

Usage

rep(x, ...)

rep.int(x, times)

rep_len(x, length.out)

Arguments

x	a vector (of any mode including a list) or a factor or (for rep only) a POSIXct or POSIXlt or Date object; or an S4 object containing such an object.
...	further arguments to be passed to or from other methods. For the internal default method these can include: times A integer vector giving the (non-negative) number of times to repeat each element if of length length(x), or to repeat the whole vector if of length 1. Negative or NA values are an error. length.out non-negative integer. The desired length of the output vector. Other inputs will be coerced to an integer vector and the first element taken. Ignored if NA or invalid. each non-negative integer. Each element of x is repeated each times. Other inputs will be coerced to an integer vector and the first element taken. Treated as 1 if NA or invalid.
times	see ....
length.out	non-negative integer: the desired length of the output vector.

rep函數有4個參數：x向量或者類向量的對象,each：x元素每個重復次數,times:each后的向量的處理，如果times是單個值，則each后的值整體重復times次數，如果是x each后的向量相等長度的向量，則對each后的每個元素重復times同一位置的元素的次數，否則會報錯；length.out指times處理后的向量最終輸出的長度，如果長於生成的向量，則補齊。也就是說rep會先處理each參數，生成一個向量X1，然后times再對X1進行處理生成X2，length.out在對X2進行處理生成最終輸出的向量X3。下面是示例：

> rep(1:4,times=c(1,2,3,4))  #與向量x等長times模式
[1] 1 2 2 3 3 3 4 4 4 4
> rep(1:4,times=c(1,2,3))  #非等長模式，出現錯誤
Error in rep(1:4, times = c(1, 2, 3)) : invalid 'times' argument
> rep(1:4,each=2,times=c(1,2,3,4)) #還是非等長模式，因為each后的向量有8位，而不是4位
Error in rep(1:4, each = 2, times = c(1, 2, 3, 4)) :
invalid 'times' argument
> rep(1:4,times=c(1,2,3,4))  #等長模式，我寫重了o(╯□╰)o
[1] 1 2 2 3 3 3 4 4 4 4
> rep(1:4,times=c(1,2,3,4),each=3) #重復的例子啊，莫拍我
Error in rep(1:4, times = c(1, 2, 3, 4), each = 3) :
invalid 'times' argument
> rep(1:4,each=2,times=1:8)   #正確值，times8位長度向量
[1] 1 1 1 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4
> rep(1:4,each=2,times=1:8,len=3)   #len的使用，循環補齊注意下
[1] 1 1 2
> rep(1:4,each=2,times=3)   #先each后times
[1] 1 1 2 2 3 3 4 4 1 1 2 2 3 3 4 4 1 1 2 2 3 3 4 4
>rep函數完畢！