[Rcpp-devel] Variable for loop

[Amina Shahzadi]

Hi Dear
This is the corresponding R code which I want to have the same result from
rcpp code.

set.seed(11)
a = matrix(runif(30), nrow=10, ncol=3)
n=10
m=3
b = array(as.double(0), dim = c(n, m, n))
for(i in 1:n){
  for(j in 1:m){
    for(q in 1:i){
      if(q==1){
        b[i, j, q] = a[i, j];
      }
      else{
        b[i, j, q] = b[i-1, j, q-1] * a[i, j];
      }
    }
  }
}


On Tue, Sep 27, 2016 at 3:22 PM, Avraham Adler <avraham.adler at gmail.com>
wrote:

> Please give a simple example of an input and its expected output.
> Unfortunately "run of a variable for loop" is too general for me to
> understand.
>
> Avi
>
> On Mon, Sep 26, 2016 at 10:07 PM, Amina Shahzadi
> <aminashahzadi at gmail.com> wrote:
> > Hi Dear
> >
> > My purpose is to make run of a variable for loop. Here I have assumed
> else
> > statement to be zero. Otherwise it could be anything for example in the
> > following code.
> > In this code, my main aim to run the slices loop according to rows.
> > does it now look ok?
> >
> >
> > Thank you
> >
> > #include <RcppArmadillo.h>
> > using namespace Rcpp;
> > using namespace RcppArmadillo;
> > //[[Rcpp::depends(RcppArmadillo)]]
> > //[[Rcpp::export]]
> > arma::cube up(arma::mat a){
> >   int m = a.n_cols;
> >   int n = a.n_rows;
> >   int p = a.n_rows;
> >   arma::cube b(n, m, p);
> >   for(int i=0; i<n; i++){
> >       for(int j=0; j<m; j++){
> >         for(int q=0; q<i; q++){
> >          if(q==0){
> >            b(i, j, q) = a(i, j);
> >          }
> >          else{
> >            b(i, j, q) = b(i-1, j, q-1) * a(i, j);
> >          }
> >       }
> >     }
> >   }
> >   return b;
> > }
> >
> > On Tue, Sep 27, 2016 at 2:51 PM, Avraham Adler <avraham.adler at gmail.com>
> > wrote:
> >>
> >> Hello.
> >>
> >> Once again, it is very unclear what you want to do. Can you please
> >> explain, in English not code what your procedure intends to do, the
> >> input you expect, and the output you expect?
> >>
> >> What it LOOKS like you want to do is to create an N x M x N cube where
> >> the first slice is your matrix and the remaining slices are all 0. If
> >> that is the case, There are much, much simpler ways to do it than to
> >> traverse all N²M cells. The following should work.
> >>
> >> #include <RcppArmadillo.h>
> >> using namespace Rcpp;
> >> using namespace RcppArmadillo;
> >> //[[Rcpp::depends(RcppArmadillo)]]
> >>
> >> //[[Rcpp::export]]
> >> arma::cube fillup(arma::mat a){
> >>   int m = a.n_cols;
> >>   int n = a.n_rows;
> >>   arma::cube C = arma::cube(n, m, n, arma::fill::zeros);
> >>
> >>   C.slice(0) = a;
> >>
> >>   return(C);
> >> }
> >>
> >> Avi
> >>
> >> On Mon, Sep 26, 2016 at 5:59 PM, Amina Shahzadi <
> aminashahzadi at gmail.com>
> >> wrote:
> >> > Hi Dear
> >> >
> >> > I have a problem in using a variable for loop in using RcppArmadillo
> >> > library.
> >> > I have pasting here my code. It is executing but not giving the same
> >> > results
> >> > as its R code version gives. The results produced by it are really
> >> > weird. I
> >> > have checked it step by step. It is because of the for (int q=0; q<i;
> >> > q++).
> >> > I request tp please help how to handle it in cpp.
> >> >
> >> > The another question is I want to multiply the cube b(i, ,) by a
> scalar.
> >> > How
> >> > can we consider the entire columns and slices of a cube for each of
> the
> >> > rows.  "b(span(i), span(), span())"  is not working for me.
> >> >
> >> > Thank you
> >> >
> >> > #include <RcppArmadillo.h>
> >> > using namespace Rcpp;
> >> > using namespace RcppArmadillo;
> >> > //[[Rcpp::depends(RcppArmadillo)]]
> >> > //[[Rcpp::export]]
> >> > arma::cube up(arma::mat a){
> >> >   int m = a.n_cols;
> >> >   int n = a.n_rows;
> >> >   int p = a.n_rows;
> >> >   arma::cube b(n, m, p);
> >> >   for(int i=0; i<n; i++){
> >> >       for(int j=0; j<m; j++){
> >> >         for(int q=0; q<i; q++){
> >> >          if(q==0){
> >> >            b(i, j, q) = a(i, j);
> >> >          }
> >> >          else{
> >> >            b(i, j, q) = 0.0;
> >> >          }
> >> >       }
> >> >     }
> >> >   }
> >> >   return b;
> >> > }
> >> >
> >> > --
> >> > Amina Shahzadi
> >
> >
> >
> >
> > --
> > Amina Shahzadi
>



-- 
*Amina Shahzadi*
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