On Tue, Sep 7, 2010 at 11:40 PM, Romain Francois
<rom...@r-enthusiasts.com> wrote:
> Le 08/09/10 06:07, Christian Gunning a écrit :
>>
>> Yes, I see the reinvent-the-wheel problem, especially after combing
>> through rcpp-devel archives some more. I admit that I don't well
>> understand the relative costs/benefits of extending the R proxy class
>> versus outsourcing to Armadillo. Two examples that come to mind are
>> Rcpp::Array and Rcpp::DataFrame.
>>
>> In the first case, could I conceivably turn an input 3D SEXP array
>> into, e.g., NumericVector( Dimension(2,3,4) ), create an arma::cube
>> out of it, process it and return?
>
> I think so. I have not tried though ... have you ?
No, not yet. I just now went mucking about through the armadillo
classes (and, by extension, the rcpp-devel archives) at Dirk's
suggestion.
>> In the second case, there's a column level but no row-level accessor
>> for the DataFrame (that I could find), nor is there a mapping into
>> Armadillo. I get the impression that DataFrame is more of a
>> convenience class for *returning* data rather than processing it?
>
> Yes. It makes it easy to create a data frame and access it by column.
>
> We'd be open to extend the interface if you provide some sort of design of
> the sort of code you'd want to write.
Yeah, I apologize - I'm just at the edge of my experience here. I
spent the last few days learning proper C++ OOP writing (as opposed to
reading) in response to your earlier comment about references. I
admit, templates are still magic to me.
I guess I'm still curious about the fundamental design goals.
RcppArmadillo allows us to easily use armadillo's rich object model,
with a wealth of object-specific methods, e.g.:
mat A = randu<mat>(5,10);
mat B = ones<mat>(5,2);
// at column 2, insert a copy of B;
A.insert_cols(2, B);
Personally, R's indexing is one of my favorite parts of the language
(and C++ indexing my least). With this in mind, I've wondered about
the possibility of rolling some sort of generic Index class that
contains enough information to do (as above):
A(aColIndex) = B;
So, if the overall goal is Simple/Reads-more-like-C++, then it's a
moot point. If something like this is worth doing, is it worth doing
for a variety of Rcpp classes? I admit that i'm not entirely clear on
the cost side of the "worth" equation here :)
Christian
> Romain
>
>> best,
>> Christian
>>
>> On Tue, Sep 7, 2010 at 5:48 PM, Dirk Eddelbuettel<e...@debian.org> wrote:
>>>
>>> On 7 September 2010 at 17:26, Christian Gunning wrote:
>>> | I was thinking about this today, and I wondered if getter/setter
>>> | functions for NumericMatrix, along with MatrixIndex classes might make
>>> | any sense, as opposed to sugar? Something like this:
>>> |
>>> | SEXP foo1( int n ){
>>> | NumericVector x(n);
>>> | MatrixIndex i(1); // row index
>>> | NumericMatrix xx(n,n) ;
>>> | // possible to assign by row or column?
>>> | for (i.index =0; i.index< n; i.index++) {
>>> | xx.Setter(i) = zeros(n) ;
>>> | }
>>> | return(xx)
>>> | }
>>> |
>>> | class MatrixIndex:
>>> | {
>>> | // use apply()'s convention of 1=row, 2=col
>>> | // row/col specification is set on creation
>>> | private:
>>> | int m_rowcol;
>>> | public:
>>> | int index;
>>> | MatrixIndex( int rowcol, int i=0) {
>>> | m_rowcol = rowcol;
>>> | index = i;
>>> | }
>>> | };
>>>
>>> I have to admit that questions like this always leads to _numeric
>>> classes_
>>> such as Armadillo or NewMat rather than our R proxy classes. Did you see
>>> what Armadillo: http://arma.sourceforge.net/docs.html#insert_rows
>>>
>>> Would that help? Passing matrices from R via Rcpp to Armadillo (and
>>> back) is
>>> pretty easy.
>>>
>>> Cheers, Dirk
>>>
>>> PS We are a little behind wrapping Armadillo 0.9.70 in RcppArmadillo but
>>> we
>>> will get there "soon".
>>>
>>>
>>> | best,
>>> | Christian
>>> |
>>> | On Sun, Aug 22, 2010 at 5:23 AM, Romain Francois
>>> |<rom...@r-enthusiasts.com> wrote:
>>> |> Hello,
>>> |>
>>> |> There currently is no sugar facility to generate a matrix the way you
>>> want.
>>> |> The last option is probably the best thing to do for now.
>>> |>
>>> |> Perhaps outer can help you :
>>> |>
>>> |> NumericVector xx(x) ;
>>> |> NumericVector yy(y);
>>> |> NumericMatrix m = outer( xx, yy, std::plus<double>() ) ;
>>> |> return m ;
>>> |>
>>> |> Romain
>>> |>
>>> |> Le 21/08/10 23:13, Christian Gunning a écrit :
>>> |>>
>>> |>> Dear list,
>>> |>>
>>> |>> I'm amazed at the ability to use the apply family in Rcpp. Yet I'm
>>> still
>>> |>> unsure of the best way to assign NumericVector objects into
>>> |>> NumericMatrix objects. Must this be done element-by-element, or is
>>> |>> there something equivalent to R's MyMatrix[,1] = MyColVector?
>>> |>> (As an aside, are both mymatrix[i,j] and mymatrix(i,j) equivalent?
>>> It
>>> |>> seems that I've seen them used interchangably on the list.)
>>> |>>
>>> |>> A simple example of what I'm aiming for:
>>> |>> Make an n*n matrix, and use sapply to perform a vector operation by
>>> |>> row, here constructing a vector of length n full of zeros.
>>> |>>
>>> |>> // a simple vector-returning function
>>> |>> NumericVector zeros( int n){
>>> |>> NumericVector ret(n);
>>> |>> ret = 0;
>>> |>> return ret;
>>> |>> }
>>> |>>
>>> |>> // sapply version, doesn't work but is easy to read
>>> |>> SEXP foo( int n ){
>>> |>> NumericVector x(n);
>>> |>> x = n;
>>> |>> NumericMatrix xx(n,n) ;
>>> |>> // possible to assign by row or column?
>>> |>> xx = sapply( x, zeros ) ;
>>> |>> return(xx);
>>> |>> }
>>> |>>
>>> |>> // the looped version, where xx[,i] is not syntactically valid
>>> |>> SEXP foo1( int n ){
>>> |>> NumericVector x(n);
>>> |>> int i;
>>> |>> NumericMatrix xx(n,n) ;
>>> |>> // possible to assign by row or column?
>>> |>> for (i =0; i<n; i++) {
>>> |>> xx[,i] = zeros(n) ;
>>> |>> }
>>> |>> return(xx)
>>> |>> }
>>> |>>
>>> |>>
>>> |>> // syntactically valid, element-wise assignment
>>> |>> SEXP foo2( int n ){
>>> |>> NumericVector x(n);
>>> |>> int i, j;
>>> |>> NumericMatrix xx(n,n) ;
>>> |>> // possible to assign by row or column?
>>> |>> for (i=0; i<n; i++) {
>>> |>> x = zeros(n) ;
>>> |>> for (j=0; j<n; j++) {
>>> |>> xx(i,j) = x[j]
>>> |>> }
>>> |>> }
>>> |>> return(xx)
>>> |>> }
>>> |>>
>>> |>> thanks so much,
>>> |>> Christian Gunning
>>> |>> --
>>> |>> A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal – Panama!
>>> |>
>>> |> --
>>> |> Romain Francois
>>> |> Professional R Enthusiast
>>> |> +33(0) 6 28 91 30 30
>>> |> http://romainfrancois.blog.free.fr
>>> |> |- http://bit.ly/bzoWrs : Rcpp svn revision 2000
>>> |> |- http://bit.ly/b8VNE2 : Rcpp at LondonR, oct 5th
>>> |> `- http://bit.ly/aAyra4 : highlight 0.2-2
>>> |>
>>> |>
>>> |
>>> |
>>> |
>>> | --
>>> | A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal – Panama!
>>> | _______________________________________________
>>> | Rcpp-devel mailing list
>>> | Rcpp-devel@lists.r-forge.r-project.org
>>> | https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
>>>
>>> --
>>> Dirk Eddelbuettel | e...@debian.org | http://dirk.eddelbuettel.com
>>>
>>
>>
>>
>
>
> --
> Romain Francois
> Professional R Enthusiast
> +33(0) 6 28 91 30 30
> http://romainfrancois.blog.free.fr
> |- http://bit.ly/bzoWrs : Rcpp svn revision 2000
> |- http://bit.ly/b8VNE2 : Rcpp at LondonR, oct 5th
> `- http://bit.ly/aAyra4 : highlight 0.2-2
>
>
>
--
A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal – Panama!
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