如何擦除行/列？
作为我学习Rcpp类/数据结构的新手问题：是否有成员函数来擦除类Rcpp::NumericMatrix的对象的行/列？ （或其他类型的type **Matrix - 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;
}')
如何使用RcppArmadillo？ 我认为代码的意图会更清晰......
#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(1:9,3), 2 )
[,1] [,2]
[1,] 1 7
[2,] 3 9
是的，这两种方法都有效（解决我上面的错误）。 我得到了一个转换错误，试图用Rcpp::NumericMatrix::iterator iter替换int iter 。 任何解决这个问题？
请注意，我们不需要row_erase(NumericMatrix& x, int& ref)因为这是row_erase(NumericMatrix& x, IntegerVector& ref) 。
NumericMatrix row_erase (NumericMatrix& x, IntegerVector& rowID) {
rowID = rowID.sort();
NumericMatrix x2(Dimension(x.nrow()- rowID.size(), x.ncol()));
int iter = 0;
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;
}
NumericMatrix col_erase (NumericMatrix& x, IntegerVector& colID) {
colID = colID.sort();
NumericMatrix x2(Dimension(x.nrow(), x.ncol()- colID.size()));
int iter = 0;
int del = 1;
for (int i = 0; i < x.ncol(); i++) {
if (i != colID[del - 1]) {
x2.col(iter) = x.column(i);
iter++;
} else {
del++;
}
}
return x2;
}