RCPP NumericMatrix-如何删除行/列?

问题描述

我学习Rcpp类/数据结构时遇到一个新手问题:是否存在一个成员函数来擦除类 Rcpp :: NumericMatrix 的对象的行/列?(或其他类型的类型**矩阵-我假设它是模板类)?

A novice question as I learn the Rcpp classes / data structures: Is there a member function to erase a row / column for an object of class Rcpp::NumericMatrix? (Or other types of type **Matrix -- I'm assuming it's a template class)?

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，怎么办?

If this type of member function doesn't exist, how about this?

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:

Or perhaps we wish to remove a set of rows/columns:

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;
}')

推荐答案

是的，这两种方法都可以工作(上面已修正我的错别字).我尝试将 int iter 替换为 Rcpp :: NumericMatrix :: iterator iter 时遇到转换错误.对此有任何解决办法吗?

Yes, both of these do work (fixing my typos above). I got a conversion error trying to replace int iter with Rcpp::NumericMatrix::iterator iter though. Any fix for this?

请注意，我们不需要 row_erase(NumericMatrix& x，int& ref)，因为这是 row_erase(NumericMatrix& x，IntegerVector& ref)的特例>.

Note that we do not need the row_erase(NumericMatrix& x, int& ref) since this is a special case of 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;
}

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