我学习Rcpp类/数据结构时的新手问题：是否有成员函数来擦除类Rcpp :: NumericMatrix对象的行/列？ (或其他类型的**矩阵 – 我假设它是一个模板类)？
library(Rcpp)
cppFunction('
NumericMatrix sub1 {NumericMatrix x,int& rowID,int& colID) {
// let's assume separate functions for rowID or colID
// but for the example case here
x.row(rowID).erase(); // ??? does this type of member function exist?
x.col(colID).erase(); // ???
return x;
}')
如果这种类型的成员函数不存在,那么这个怎么样？
cppFunction('NumericMatrix row_erase (NumericMatrix& x,int& rowID) {
// a similar function would exist for removing a column.
NumericMatrix x2(Dimension(x.nrow()-1,x.ncol());
int iter = 0; // possibly make this a pointer?
for (int i = 0; i < x.nrow(); i++) {
if (i != rowID) {
x2.row(iter) = x.row(i);
iter++;
}
}
return x2;
}')
或者我们希望删除一组行/列：
cppFunction('NumericMatrix row_erase (NumericMatrix& x,IntegerVector& rowID) {
// a similar function would exist for removing a column.
rowID = rowID.sort();
NumericMatrix x2(Dimension(x.nrow()- rowID.size(),x.ncol());
int iter = 0; // possibly make this a pointer?
int del = 1; // to count deleted elements
for (int i = 0; i < x.nrow(); i++) {
if (i != rowID[del - 1])
x2.row(iter) = x.row(i);
iter++;
} else {
del++;
}
}
return x2;
}')
解决方法
使用RcppArmadillo怎么样？我认为代码的意图会更清楚……
#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]
using namespace arma;
// [[Rcpp::export]]
mat sub1( mat x,uword e) {
x.shed_col(e-1);
x.shed_row(e-1);
return x;
}
/*** R
sub1( matrix(1:9,3),2 )
*/
> sub1( matrix(1:9,2 )
[,1] [,2]
[1,] 1 7
[2,] 3 9
