Le 13/12/12 17:29, Dirk Eddelbuettel a écrit :
On 13 December 2012 at 10:01, Romain Francois wrote:
| Hello,
|
| I'd like to add a functionality to "bind" vectors of the same type (well
| sugar expressions really, but let's say it is vectors for the sake of
| this email).
|
| So essentially I'd like something similar to what "c" does in R :
|
| > c( letters, letters )
| [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p"
| "q" "r" "s"
| [20] "t" "u" "v" "w" "x" "y" "z" "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
| "k" "l"
| [39] "m" "n" "o" "p" "q" "r" "s" "t" "u" "v" "w" "x" "y" "z"
|
|
| I don't want to call it "c", and I'd like suggestions : combine, bind ?
|
| The idea is to avoid writing code like this:
|
| CharacterVector x, y ;
| CharacterVector z( x.size() + y.size() ) ;
| int i=0;
| for( ; i<x.size(); i++) z[i] = x[i] ;
| for( int j=0; j<y.size(); i++, j++) z[i] = y[j] ;
|
| I know it is not a big deal for people to write this code, but for
| example this does not handle the names of the elements, ... and
| internally I can use more efficient code
The STL more or less has that already, just combine two calls to copy():
-----------------------------------------------------------------------------
#include <Rcpp.h>
// [[Rcpp::export]]
std::vector<std::string> concat(std::vector<std::string> x,
std::vector<std::string> y) {
std::vector<std::string> z(x.size() + y.size());
std::copy(x.begin(), x.end(), z.begin());
std::copy(y.begin(), y.end(), z.begin() + x.size());
return(z);
}
/*** R
concat(letters[1:5], letters[1:4])
***/
-----------------------------------------------------------------------------
R> sourceCpp("/tmp/concat.cpp")
R> concat(letters[1:5], letters[1:4])
[1] "a" "b" "c" "d" "e" "a" "b" "c" "d"
R>
Dirk
I'm not asking how to implement it, I have a fairly good understanding
of std::copy.
I was just asking how to name this.
I'd like to have, e.g. the possibility to do:
CharacterVector x, y ; // from somewhere
CharacterVector z1 = concat(x, y ) ;
CharacterVector z1 = concat(x, "foo", y ) ;
Or perhaps dealing with sugar exprs;
CharacterVector z1 = concat( rep(x, 2), rep_each(y, 3) ) ;
... anyway. I think I like "concat"
Romain
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
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blog: http://romainfrancois.blog.free.fr
|- http://bit.ly/RE6sYH : OOP with Rcpp modules
`- http://bit.ly/Thw7IK : Rcpp modules more flexible
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