[Rcpp-devel] Efficient DataFrame access by row & column

[Kevin Ushey]

Another thing worth thinking about: perhaps the easiest way to side-step
the issue is to work with a NumericMatrix rather than a DataFrame. At
least, from the example you gave, it sounds like a container where you have
the expectation that each column is a NumericVector of equal length.

If you can make the switch to NumericMatrix, then you can generate and
operate with row/column views, e.g. NumericMatrix::Row and
NumericMatrix::Column, which will generate references to rows / columns and
hence avoid copying. (These are generated whenever you do e.g. x(i, _) or
x(_, i) on a NumericMatrix x).

-Kevin

On Tue, Feb 19, 2013 at 3:26 PM, Ken Williams
<Ken.Williams at windlogics.com>wrote:

>
>
> > From: John Merrill [mailto:john.merrill at gmail.com]
> > Sent: Tuesday, February 19, 2013 5:24 PM
> > To: Ken Williams
> > Cc: Yan Zhou; Dirk Eddelbuettel; rcpp-devel at lists.r-forge.r-project.org
> > Subject: Re: [Rcpp-devel] Efficient DataFrame access by row & column
> >
> > I'm a little puzzled by your question.  Could you use a reference
> instead of instantiating a new copy?
>
> I would love to use a reference, but I don't know how.  That's in fact the
> essence of my question. =)
>
> Is there already some example code somewhere showing how to get reference
> to a DataFrame column without copying?  I must be just missing it.
>
>  -Ken
>
>
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