Re: [igraph] How to pass graphs from R to C extensions? .C or .Call ?

[Aaron McDaid]

Hi,
That makes more sense to me now. The version of igraph_0.5.2-2.tgz
that I had previously downloaded did not have a file called
src/rinterface.c. I thought I had downloaded the source version, but I
had just downloaded the binary. Silly mistake.

Thanks,
Aaron

On Mon, Jun 29, 2009 at 07:18, Gábor Csárdi<address@hidden> wrote:
> Hi,
>
> while theoretically it is possible to use the .C interface to pass
> igraph graphs to C code, in practice it is not. You need to use the
> .Call interface.
>
> There are plenty of examples on how to do this in the igraph source
> code. Check Rinterface.c, that contains the glue functions between R
> and the C library. The C code for the function itself should not
> contain any R-specific code.
>
> Best,
> Gabor
>
> On Sun, Jun 28, 2009 at 7:03 PM, Aaron McDaid<address@hidden> wrote:
>> Hi,
>> I hope you can spare a few minutes to help me with this. I'm trying to
>> use the .C interface in R to access simple properties such as the
>> vcount of a graph. This is just a toy exercise at first. The .Call
>> interface looks a little complicated and risky; is it possible to
>> efficiently access graphs using R's   .C interface? Or will I have to
>> use .Call and SEXPs, as per
>> http://lists.gnu.org/archive/html/igraph-help/2007-08/msg00007.html ?
>>
>> What types should I have in my C code? I've tried   const igraph_t
>> **graph  also, without success? And am I using the correct parameters
>> to the .C function in R?
>>
>> Here's my C code:
>>  void vertices_count(const igraph_t *graph, int *n) {
>>        Rprintf("graph: %p\n", graph);
>>        Rprintf("graph: %p\n", *graph);
>>        igraph_integer_t vc = igraph_vcount(graph);
>>        int vci = vc;
>>        Rprintf("vcount: %ld\n", vci);
>>        Rprintf("vcount: %ld\n", graph->n);
>>        *n=9;
>>  }
>>
>> And what happens in R:
>>> library(igraph)
>>> dyn.load("R/myRextension.so"); .C ("vertices_count", raf, 
>>> as.integer(0))[[2]]
>> graph: 0x156f0a8
>> graph: 0x14a1128
>> vcount: 0
>> vcount: 21631272
>> [1] 9
>>>
>>
>> As you can see, I'm able to call a simple function and return a simple
>> dummy answer (9). However, my C code is unable to get the vertex count
>> of the graph (which is 91707 by the way).
>>
>> - Mac OS X 10.5.7 on an iMac.
>> - R version 2.9.0 (2009-04-17)
>> - igraph 0.5.2
>>
>> Background:
>> I'm hoping to write some C extensions to igraph in R (perhaps for
>> inclusion in igraph proper in future), such as new community finding
>> algorithms, as part of my PhD. I'll be developing them mostly in R
>> itself initially, but would like to make fast C/C++ implementations
>> available in R, when appropriate.
>>
>> Thanks,
>> Aaron McDaid
>> PhD student, just started in UCD, Dublin
>> http://www.cliquecluster.org/
>> www.aaronmcdaid.com
>>
>>
>> _______________________________________________
>> igraph-help mailing list
>> address@hidden
>> http://lists.nongnu.org/mailman/listinfo/igraph-help
>>
>
>
>
> --
> Gabor Csardi <address@hidden>     UNIL DGM
>
>
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