如何在使用 Eigen Library c++ 时删除特定的行或列

Question

我正在为我的项目使用 Eigen 库。我正在搜索如何从 Eigen 中的给定矩阵中删除特定的行或列。我没有成功。

MatrixXd A = X1 X2 X3 X4
             Y1 Y2 Y3 Y4
             Z1 Z2 Z3 Z4
             A1 A2 A3 A4
MatrixXd Atransform = X1 X2 X4
                      Y1 Y2 Y4
                      Z1 Z2 Z4
                      A1 A2 A4
enter code here

除了遍历整个矩阵或对矩阵 A 使用块操作。有没有简单的方法。

Answer 1

使用块函数更简洁：

void removeRow(Eigen::MatrixXd& matrix, unsigned int rowToRemove)
{
    unsigned int numRows = matrix.rows()-1;
    unsigned int numCols = matrix.cols();

    if( rowToRemove < numRows )
        matrix.block(rowToRemove,0,numRows-rowToRemove,numCols) = matrix.block(rowToRemove+1,0,numRows-rowToRemove,numCols);

    matrix.conservativeResize(numRows,numCols);
}

void removeColumn(Eigen::MatrixXd& matrix, unsigned int colToRemove)
{
    unsigned int numRows = matrix.rows();
    unsigned int numCols = matrix.cols()-1;

    if( colToRemove < numCols )
        matrix.block(0,colToRemove,numRows,numCols-colToRemove) = matrix.block(0,colToRemove+1,numRows,numCols-colToRemove);

    matrix.conservativeResize(numRows,numCols);
}

Answer 2

使用 Eigen 3.3.0+（2016.08 发布）可以更轻松、更短地完成此操作：

vector<int> indicesToKeep = vector<int>{ 1, 2, 3 };
VectorXi indicesToKeepVector = VectorXi(indicesToKeep.data(), indicesToKeep.size());
MatrixXf matrix = MatrixXf(); // your data should be here!
matrix = matrix(Eigen::placeholders::all, indicesToKeepVector); // select columns you want to keep(indicesToKeep), discard others
matrix = matrix(indicesToKeepVector, Eigen::placeholders::all); // select rows you want to keep(indicesToKeep), discard others
matrix = matrix(Eigen::seq(5, 10), Eigen::placeholders::all); // keep rows from 5 to 10
matrix = matrix(Eigen::placeholders::all, Eigen::seq(5, 10)); // keep columns from 5 to 10
matrix = matrix(Eigen::seqN(5, 5), Eigen::placeholders::all); // keep rows from 5 to 10
matrix = matrix(Eigen::placeholders::all, Eigen::seqN(5, 5)); // keep columns from 5 to 10

Answer 3

要改进 Andrew 的答案，请使用 bottomRows/rightCols。

void removeRow(Eigen::MatrixXd& matrix, unsigned int rowToRemove)
{
    unsigned int numRows = matrix.rows()-1;
    unsigned int numCols = matrix.cols();

    if( rowToRemove < numRows )
        matrix.block(rowToRemove,0,numRows-rowToRemove,numCols) = matrix.bottomRows(numRows-rowToRemove);

    matrix.conservativeResize(numRows,numCols);
}

void removeColumn(Eigen::MatrixXd& matrix, unsigned int colToRemove)
{
    unsigned int numRows = matrix.rows();
    unsigned int numCols = matrix.cols()-1;

    if( colToRemove < numCols )
        matrix.block(0,colToRemove,numRows,numCols-colToRemove) = matrix.rightCols(numCols-colToRemove);

    matrix.conservativeResize(numRows,numCols);
}

Answer 4

您可能会发现以下静态版本更适合某些用途（并且更符合 Eigen 编译时效率的精神）。在这种情况下，您将创建一个没有行的新矩阵。可以使用.leftCols() .rightCols()为列构造类似的函数

template<typename T>
inline constexpr auto removeRow(const Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic>& matrix, const int& rowNum)
{
    return (Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic>(matrix.rows() - 1, matrix.cols())
        << static_cast<Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic>>(matrix.topRows(rowNum - 1)),
        static_cast<Eigen::Matrix<T, Eigen::Dynamic, Eigen::Dynamic>>(matrix.bottomRows(matrix.rows() - rowNum))).finished();
}

享受吧！

Answer 5

我知道这是一个老问题，但似乎 Eigen 现在支持创建由索引的行和列定义的子矩阵： http://eigen.tuxfamily.org/bz/show_bug.cgi?id=329 http://eigen.tuxfamily.org/dox-devel/classEigen_1_1DenseBase.html#a0b44220621cd59a75cd0f48cc499518f

它似乎不在文档中......

Answer 6

  inline Eigen::MatrixXd removeMatrixRow(const Eigen::MatrixXd original_matrix, const int row_to_remove)
  {
    // New matrix has one fewer rows
    Eigen::MatrixXd new_matrix(original_matrix.rows()-1, original_matrix.cols());
    // Track rows in new matrix. Skip one at row_to_remove.
    int row_to_fill = 0;
    for (int orig_matrix_row = 0; orig_matrix_row < original_matrix.rows(); ++orig_matrix_row)
    {
      if (orig_matrix_row != row_to_remove)
      {
        new_matrix.row(row_to_fill) = original_matrix.row(orig_matrix_row);
        ++row_to_fill;
      }
    }
    return new_matrix;
  }

Answer 7

我是 C++ 新手，但此代码适用于可能的应用程序。

它只适用于全动态矩阵，但可以适应它。

如果有人有更好的方法，请告诉我我真的很想学习。

template<typename ScalarType>
void MatrixXdRemoveCol(Eigen::Matrix<ScalarType,-1,-1,0,-1,-1> *mat, int colindex)
{
    Eigen::Matrix<ScalarType,-1,-1,0,-1,-1> *auxmat = new Eigen::Matrix<ScalarType,-1,-1,0,-1,-1>;

    *auxmat = *mat;

    mat->resize(mat->rows(),mat->cols()-1);

    int rightColsSize = auxmat->cols()-colindex-1;

    mat->leftCols(colindex) = auxmat->leftCols(colindex);
    mat->rightCols(rightColsSize) = auxmat->rightCols(rightColsSize);
}

template<typename ScalarType>
void MatrixXdRemoveCols(Eigen::Matrix<ScalarType,-1,-1,0,-1,-1> *mat, std::vector<int>* cols)
{
    for(auto iter = cols->rbegin();iter != cols->rend();iter++)
        MatrixXdRemoveCol<ScalarType>(mat,*iter);
}

template<typename ScalarType>
void MatrixXdRemoveRow(Eigen::Matrix<ScalarType,-1,-1,0,-1,-1> *mat, int rowindex)
{
    Eigen::Matrix<ScalarType,-1,-1,0,-1,-1> *auxmat = new Eigen::Matrix<ScalarType,-1,-1,0,-1,-1>;

    *auxmat = *mat;

    mat->resize(mat->rows()-1,mat->cols());

    int BottomRowsSize = auxmat->rows()-rowindex-1;

    mat->topRows(rowindex) = auxmat->topRows(rowindex);
    mat->bottomRows(BottomRowsSize) = auxmat->bottomRows(BottomRowsSize);
}