从 R 对象中提取 long[] [英] Extract long[] from R object

问题描述

我正在尝试为一些基于 C 的稀疏矩阵处理代码制作一个包装器(参见 上一个问题).为了调用主力 C 函数，我需要创建一个如下所示的结构:

I'm trying to make a wrapper for some C-based sparse-matrix-handling code (see previous question). In order to call the workhorse C function, I need to create a structure that looks like this:

struct smat {
  long rows;
  long cols;
  long vals;     /* Total non-zero entries. */
  long *pointr;  /* For each col (plus 1), index of first non-zero entry. */
  long *rowind;  /* For each nz entry, the row index. */
  double *value; /* For each nz entry, the value. */
};

这些很好地对应于 dgCMatrix 稀疏矩阵.所以理想情况下，我只指向 dgCMatrix 中的内部数组(在验证 C 函数不会处理数据 [我还没有完成] 之后).

These correspond nicely to the slots in a dgCMatrix sparse matrix. So ideally I'd just point to the internal arrays in the dgCMatrix (after verifying that the C function won't twiddle with the data [which I haven't done yet]).

对于*value，看起来我可以使用REALSXP 或其他东西来根据需要获得double[].但是对于 *pointr 和 *rowind，我不确定获得适当数组的最佳方法.我是否需要遍历条目并将它们复制到新数组中，一边进行一边转换?或者 Rcpp 可以在这里提供一些糖吗?这是我第一次真正使用 Rcpp，但我还不是很熟悉.

For *value, it looks like I'll be able to use REALSXP or something to get a double[] as desired. But for *pointr and *rowind, I'm not sure the best way to get at an appropriate array. Will I need to loop through the entries and copy them to new arrays, casting as I go? Or can Rcpp provide some sugar here? This is the first time I've really used Rcpp much and I'm not well-versed in it yet.

谢谢.

我也遇到了一些我不明白的链接问题:

I'm also having some linking trouble that I don't understand:

Error in dyn.load(libLFile) : 
  unable to load shared object '/var/folders/TL/TL+wXnanH5uhWm4RtUrrjE+++TM/-Tmp-//RtmpAA9upc/file2d4606aa.so':
  dlopen(/var/folders/TL/TL+wXnanH5uhWm4RtUrrjE+++TM/-Tmp-//RtmpAA9upc/file2d4606aa.so, 6): Symbol not found: __Z8svdLAS2AP4smatl
  Referenced from: /var/folders/TL/TL+wXnanH5uhWm4RtUrrjE+++TM/-Tmp-//RtmpAA9upc/file2d4606aa.so
  Expected in: flat namespace
 in /var/folders/TL/TL+wXnanH5uhWm4RtUrrjE+++TM/-Tmp-//RtmpAA9upc/file2d4606aa.so

我是否需要使用一些特殊的编译标志来创建我的库?

Do I need to be creating my library with some special compilation flags?

编辑 2:看起来我的 libargs 参数没有效果，所以 libsvd 符号永远不会进入库.我找不到使用 cxxfunction() 包含库的方法 - 这是我尝试过的，但额外的参数(一厢情愿地从 cfunction() 借来)是默默吞了下去:

Edit 2: it looks like my libargs parameter has no effect, so libsvd symbols never make it into the library. I can find no way to include libraries using cxxfunction() - here's what I'd tried, but the extra parameters (wishful-thinkingly-borrowed from cfunction()) are silently gobbled up:

fn <- cxxfunction(sig=c(nrow="integer", mi="long", mp="long", mx="numeric"), 
                  body=code,
                  includes="#include <svdlib.h>\n", 
                  cppargs="-I/Users/u0048513/Downloads/SVDLIBC", 
                  libargs="-L/Users/u0048513/Downloads/SVDLIBC -lsvd", 
                  plugin="Rcpp",
                  verbose=TRUE)

我觉得我的整个过程都是错误的，因为没有任何效果.有人朝正确的方向踢我吗?

I feel like I'm going about this whole process wrong, since nothing's working. Anyone kick me in the right direction?

推荐答案

我决定也在 Rcpp-devel 邮件列表上发布一个查询，并得到了一些很好的建议 &来自德克和道格的帮助:

I decided to also post a query on the Rcpp-devel mailing list, and got some good advice & help from Dirk and Doug:

http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2011-February/001851.html

我对这些东西仍然不是很容易，但是已经到了.=)

I'm still not super-facile with this stuff, but getting there. =)

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