template<typename XprType, int Rows, int Cols, int Order>
class Eigen::Reshaped< XprType, Rows, Cols, Order >

Expression of a fixed-size or dynamic-size reshape.

Template Parameters

XprType	the type of the expression in which we are taking a reshape
Rows	the number of rows of the reshape we are taking at compile time (optional)
Cols	the number of columns of the reshape we are taking at compile time (optional)
Order	can be ColMajor or RowMajor, default is ColMajor.

This class represents an expression of either a fixed-size or dynamic-size reshape. It is the return type of DenseBase::reshaped(NRowsType,NColsType) and most of the time this is the only way it is used.

However, in C++98, if you want to directly maniputate reshaped expressions, for instance if you want to write a function returning such an expression, you will need to use this class. In C++11, it is advised to use the auto keyword for such use cases.

Here is an example illustrating the dynamic case:

#include <Eigen/Core>
#include <iostream>
using namespace std;
using namespace Eigen;
 
template<typename Derived>
const Reshaped<const Derived>
reshape_helper(const MatrixBase<Derived>& m, int rows, int cols)
{
  return Reshaped<const Derived>(m.derived(), rows, cols);
}
 
int main(int, char**)
{
  MatrixXd m(3, 4);
  m << 1, 4, 7, 10,
       2, 5, 8, 11,
       3, 6, 9, 12;
  cout << m << endl;
  Ref<const MatrixXd> n = reshape_helper(m, 2, 6);
  cout << "Matrix m is:" << endl << m << endl;
  cout << "Matrix n is:" << endl << n << endl;
}

Output:

 1  4  7 10
 2  5  8 11
 3  6  9 12
Matrix m is:
 1  4  7 10
 2  5  8 11
 3  6  9 12
Matrix n is:
 1  3  5  7  9 11
 2  4  6  8 10 12

Here is an example illustrating the fixed-size case:

#include <Eigen/Core>
#include <iostream>
using namespace Eigen;
using namespace std;
 
template<typename Derived>
Eigen::Reshaped<Derived, 4, 2>
reshape_helper(MatrixBase<Derived>& m)
{
  return Eigen::Reshaped<Derived, 4, 2>(m.derived());
}
 
int main(int, char**)
{
  MatrixXd m(2, 4);
  m << 1, 2, 3, 4,
       5, 6, 7, 8;
  MatrixXd n = reshape_helper(m);
  cout << "matrix m is:" << endl << m << endl;
  cout << "matrix n is:" << endl << n << endl;
  return 0;
}

Output:

matrix m is:
1 2 3 4
5 6 7 8
matrix n is:
1 3
5 7
2 4
6 8

See also

DenseBase::reshaped(NRowsType,NColsType)