如何在Rcpp中创建向量列表?

I'm writing an Rcpp module an would like to return as one element of the RcppResultSet list a list whose elements are vectors. E.g., .Call("myfunc")$foo should be something like:

我正在编写一个Rcpp模块，希望作为RcppResultSet列表中的一个元素返回一个元素是向量的列表。例如:. call ("myfunc")$foo应该是:

[[1]]
[1] 1

[[2]]
[1] 1 1

[[3]]
[1] 1 1 1

(the exact numbers are not important here). The issue is that I don't know the right Rcpp way of doing this. I tried passing a vector<vector<int> > but this constructs a matrix by silently taking the length of the first vector as the width (even if the matrix is ragged!). I've tried constructing an RcppList but have a hard time casting various objects (like RcppVector) safely into SEXPs.

(确切的数字在这里并不重要)。问题是我不知道正确的Rcpp方法。我试过传递一个向量 <矢量 >，但这是通过将第一个向量的长度作为宽度(即使这个矩阵是粗糙的!)来构造一个矩阵。我试过构造一个RcppList，但是很难将各种对象(比如RcppVector)安全地转换为SEXPs。

Anyone have tips on best practices for dealing with complicated structures such as lists of vectors in Rcpp?

任何人都有关于处理复杂结构的最佳实践的技巧，比如Rcpp中的向量列表?

2 个解决方案

#1

[ Nice to see this here but Romain and I generally recommend the rccp-devel list for question. Please post there going forward as the project is not yet that large it warrants to have questions scattered all over the web. ]

很高兴看到这个，但罗曼和我通常推荐rccp-devel列表。当项目还没有那么大的时候，请张贴在那里，并保证有问题散布在网上。]

RcppResultSet is part of the older classic API whereas a lot of work has gone into what we call the new API (starting with the 0.7.* releases). Have a look at the current Rcpp page on CRAN and the list of vignettes -- six and counting.

RcppResultSet是旧的经典API的一部分，而大量的工作已经进入了我们所称的新API(从0.7开始)。*版本)。看一下CRAN的当前Rcpp页面，以及“vignettes”的列表——6个，然后计数。

With new API you would return something like

使用新的API，你会返回一些类似的东西。

return Rcpp::List::create(Rcpp::Named("vec") = someVector,
                          Rcpp::Named("lst") = someList,
                          Rcpp::Named("vec2") = someOtherVector);

all in one statement (and possibly using explicit Rcpp::wrap() calls), creating what in R would be

在一个语句中(并且可能使用显式Rcpp::wrap()调用)，创建在R中将会是什么。

list(vec=someVector, lst=someList, vec2=someOtherVector)

And Rcpp::List should also be able to do lists of lists of lists... though I am not sure we have unit tests for this --- but there are numerous examples in the 500+ unit tests.

列表还应该可以列出列表的列表…虽然我不确定我们是否有单元测试，但是在500+单元测试中有很多例子。

As it happens, I spent the last few days converting a lot of RQuantLib code from the classic API to the new API. This will probably get released once we get version 0.8.3 of Rcpp out (hopefully in a few days). In the meantime, you can look at the RQuantLib SVN archive

当它发生时，我花了几天时间将许多RQuantLib代码从经典API转换为新的API。一旦我们得到Rcpp的0.8.3版本(希望在几天内)，这可能会得到释放。同时，您可以查看RQuantLib SVN存档。

#2

I would tend to use a compressed variation of Dirk's solution:

我倾向于使用德克的解决方案的压缩版本:

using namespace Rcpp ;
return List::create( 
   _["vec"]  = someVector, 
   _["lst"]  = someList, 
   _["vec2"] = someOtherVector
 ) ;

Also, to come back to the original question, vector< vector<int> > should wrap itself to a list of integer vectors, not a matrix. See:

同样，回到最初的问题，向量 <向量 >应该把自己包装成一个整数向量的列表，而不是一个矩阵。看到的:

require( Rcpp )
require( inline )
require( RUnit )

fx <- cxxfunction( , '

    std::vector< std::vector<int> > v ;

    std::vector<int> x1(1) ; v.push_back( x1 );
    std::vector<int> x2(2) ; v.push_back( x2 );
    std::vector<int> x3(3) ; v.push_back( x3 );

    return wrap( v ) ;

', plugin = "Rcpp" )

I get :

我得到:

> fx() 

[[1]]
[1] 0

[[2]]
[1] 0 0

[[3]]
[1] 0 0 0

#1