[Rcpp-devel] Data Persistence when using inline

Noah Silverman noahsilverman at ucla.edu
Thu Sep 8 00:04:18 CEST 2011


Maybe I didn't explain it well enough.  The question absolutely pertains to using the inline functionality.

As each new data arrives, I want to pass it to my C++ function.  If this were a pure C++ implementation, then I would just append an STL vector and pass a pointer of that vector to the function.  However, since this is R, I don't see how to do that.  I can, of course, keep a vector in R and pass the entire vector to the C++ function. That will, however slow things down significantly.

Ultimately, I'dl like to have R pass each new data point to the C++ function, and have that function manage keeping the appropriate length window of past data points. (Again, trivial to do in pure C++).

This really is an issue of persistent object and passing between R and C++.  I want a persistent C++ vector, not an R data structure.  (Having C++ manage the vector will be much faster.)

Noah Silverman
UCLA Department of Statistics
8117 Math Sciences Building #8208
Los Angeles, CA 90095

On Sep 7, 2011, at 2:56 PM, Dirk Eddelbuettel wrote:

> On 7 September 2011 at 14:46, Noah Silverman wrote:
> | Hi,
> | 
> | 
> | I'm writing a function using Rcpp through inline.  This function will be a
> | filter on an incoming data stream.  
> | 
> | I need to keep the past several data values so that they are accessible to the
> | function each time it is called.   This is easy to do with a data structure in
> | R (and then passing subsequent structure to the C++ function) but that seems
> | rather slow.  Is there some way to define a persistent object that is
> | accessible to an Inline function using Rcpp?
> | 
> | 
> | If the code was in pure C++, it would be trivial to have an object and then
> | just pass a pointer to that object.  I can't figure out how to do the same
> | thing with R+Rcpp+inline.
> i)   Read up on the 'static' argument for variable declarations in C and C++.
> ii)  Rethink your architecture, maybe have an 'agent' operate on the stream
>     and report to a persisting 'broker' that keeps state.
> iii) Read up on persisting data as a general issue.
> This has little to do with Rcpp and your preference of inline over packages,
> but rather with how to think in code (and/or C++) and that is NOT a topic
> covered on this list.  
> Let's please try to keep focus on Rcpp and related questions here.
> Dirk
> | Thanks!
> | 
> | --
> | Noah Silverman
> | UCLA Department of Statistics
> | 8117 Math Sciences Building #8208
> | Los Angeles, CA 90095
> | 
> | 
> | ----------------------------------------------------------------------
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> -- 
> Two new Rcpp master classes for R and C++ integration scheduled for 
> New York (Sep 24) and San Francisco (Oct 8), more details are at
> http://dirk.eddelbuettel.com/blog/2011/08/04#rcpp_classes_2011-09_and_2011-10
> http://www.revolutionanalytics.com/products/training/public/rcpp-master-class.php

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