循环通过向量 [英] Cycling through a vector

问题描述

我想知道是否可以在 R 中做到这一点:

I was wondering if it is possible in R to do it:

1. 我有一个 list <- c(x1, x2, x3, x4, xn...)
2. 使用 for 循环，将 x1 放在列表的底部，给出 c(x2, x3, x4, xn.. x1).
3. 下一个循环将是 c(x3, x4, x5... x1, x2)

1. I have a list <- c(x1, x2, x3, x4, xn...)
2. With a for loop, put x1 at the bottom of the list giving c(x2, x3, x4, xn.. x1).
3. Next loop would be c(x3, x4, x5... x1, x2)

这在 R 中可行吗?

推荐答案

我不知道你想做什么，但在下面的例子中，你可以看到"(print) 循环在每次运行中的作用:

I don't know what you're trying to do, but in the following example, you can "see" (print) what the loop does in each run:

#a vector (and not list)
vec <- c(5:10) 

#the loop
for(i in seq_along(vec)) { print(c(vec[-(0:i)], vec[0:i])) }

#[1]  6  7  8  9 10  5
#[1]  7  8  9 10  5  6
#[1]  8  9 10  5  6  7
#[1]  9 10  5  6  7  8
#[1] 10  5  6  7  8  9
#[1]  5  6  7  8  9 10  

如果您想存储输出而不仅仅是查看它，请考虑:

If you want to store the output and not just to see it, then consider this:

> result <- vector("list", length(vec))
> for(i in seq_along(vec)) { 
    result[[i]] <- c(vec[-(0:i)], vec[0:i])
  }
> 
> do.call(rbind, result)
     [,1] [,2] [,3] [,4] [,5] [,6]
[1,]    6    7    8    9   10    5
[2,]    7    8    9   10    5    6
[3,]    8    9   10    5    6    7
[4,]    9   10    5    6    7    8
[5,]   10    5    6    7    8    9
[6,]    5    6    7    8    9   10

为了避免列表中的预分配和for循环和最后的rbinding，sapply是不错的选择

In order to avoid pre-allocation in a list and the for loop and rbinding at the end, sapply is good option

sapply(1:length(vec), function(i) c(vec[-(0:i)], vec[0:i]))

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