如何在 Rcpp 中创建向量列表? [英] How do I create a list of vectors in Rcpp?

问题描述

我正在编写一个 Rcpp 模块，我想返回一个元素为向量的列表作为 RcppResultSet 列表的一个元素.例如，.Call("myfunc")$foo 应该是这样的:

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:

[[1]]
[1] 1

[[2]]
[1] 1 1

[[3]]
[1] 1 1 1

(这里的确切数字并不重要).问题是我不知道这样做的正确 Rcpp 方式.我尝试传递一个 vector;> 但这通过默默地将第一个向量的长度作为宽度来构造一个矩阵(即使矩阵是参差不齐的！).我已经尝试构建一个 RcppList，但很难将各种对象(如 RcppVector)安全地投射到 SEXPs 中.

(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.

任何人都知道处理复杂结构(例如 Rcpp 中的向量列表)的最佳实践技巧?

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

推荐答案

[ 很高兴在这里看到这个，但 Romain 和我通常推荐 rccp-devel 问题列表.请在那里发布，因为该项目还没有那么大，所以问题分散在整个网络上.]

[ 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. ]

RcppResultSet 是旧的经典 API 的一部分，而我们称之为新 API(从0.7.* 版本).看看当前的 CRAN 上的 Rcpp 页面 和小插曲列表——六个和数数.

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.

使用新 API，您将返回类似

With new API you would return something like

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

全部在一个语句中(并且可能使用显式的 Rcpp::wrap() 调用)，在 R 将是

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

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

和 Rcpp::List 也应该能够做列表列表的列表......虽然我不确定我们是否有单元测试 --- 但有很多例子在500 多个单元测试.

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.

碰巧的是，过去几天我花了很多时间转换RQuantLib 代码从经典 API 到新 API.一旦我们获得 Rcpp 的 0.8.3 版(希望在一个几天).同时，您可以查看 RQuantLibSVN存档

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

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