在 R 中向量化 rep 和 seq [英] Vectorizing rep and seq in R

问题描述

我正在努力完成两件事.首先，如果我有一个向量 1:5 我想得到一个矩阵(或两个向量)，指示这些元素的唯一组合，包括两倍相同的数字但不包括重复.

I am trying to accomplish two things. First if I have a vector 1:5 I want to get a matrix (or two vectors) indicating the unique combinations of these elements including twice the same number but excluding repetitions.

现在我可以使用矩阵来做到这一点:

Right now I can do this using a matrix:

foo <- matrix(1:5,5,5)
cbind(foo[upper.tri(foo,diag=TRUE)],foo[lower.tri(foo,diag=TRUE)])
      [,1] [,2]
 [1,]    1    1
 [2,]    1    2
 [3,]    2    3
 [4,]    1    4
 [5,]    2    5
 [6,]    3    2
 [7,]    1    3
 [8,]    2    4
 [9,]    3    5
[10,]    4    3
[11,]    1    4
[12,]    2    5
[13,]    3    4
[14,]    4    5
[15,]    5    5

但必须有更简单的方法.我试图在 seq 上使用 Vectorize 但这给了我一个错误:

But there has to be a simpler way. I tried to use Vectorize on seq but this gives me an error:

cbind(Vectorize(seq,"from")(1:5,5),Vectorize(seq,"to")(5,1:5))
    Error in Vectorize(seq, "from") : 
      must specify formal argument names to vectorize

我想做的第二件事是，如果我有一个包含向量的列表，bar，以获得一个包含重复的列表元素的向量，该元素的数量等于该元素中的元素数.我可以这样做:

A second thing I want to do is if I have a list containing vectors, bar, to get a vector containing the elements of the list repeated equal to the number of elements in that element. I can do this with:

unlist(apply(rbind(1:length(bar),sapply(bar,length)),2,function(x)rep(x[1],x[2])))
 [1] 1 1 1 1 1 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3 3

但同样必须有更简单的方法.我在这里再次尝试了 Vectorize 但出现了同样的错误:

But again there must be an easier way. I tried Vectorize again here but with the same error:

Vectorize(rep,"each")(1:length(bar),each=sapply(bar,length))
 in Vectorize(rep, "each") : 
  must specify formal argument names to vectorize

推荐答案

对于你的第一个问题:base 中简单的 combn() 函数怎么样:

To your first question: what about the simple combn() function in base:

> combn(1:5,2)
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    1    1    1    2    2    2    3    3     4
[2,]    2    3    4    5    3    4    5    4    5     5

如果你需要一个矩阵排列你所组成的矩阵，只需用t()转置它，比如t(combn(1:5,2))

If you need a matrix arranged the one you made up, just transpose it with t(), like t(combn(1:5,2))

注意:这将不会返回序列中重复元素的组合，但您可以轻松地将它们添加到矩阵中.

Note: this will not give you back the combinations of repeated elements of your seq, but you may add those easily to the matrix.

这篇关于在 R 中向量化 rep 和 seq的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！