Eigen3: Matrix row and column names

Question

In R, I can name the rows and columns of a matrix:

A = matrix( 
  c(2, 4, 3, 1, 5, 7), # the data elements 
  nrow=2,              # number of rows 
  ncol=3,              # number of columns 
  byrow = TRUE)        # fill matrix by rows 

> A                      # print the matrix 

      [,1] [,2] [,3] 
[1,]    2    4    3 
[2,]    1    5    7 

dimnames(A) = list( 
  c("row1", "row2"),         # row names 
  c("col1", "col2", "col3")) # column names

> A                 # print A 
     col1 col2 col3 
row1    2    4    3 
row2    1    5    7 

How do I give row and column names to an Eigen3 Matrix from c++?

Answer 1

What I did since it doesn't appear that Eigen supports column and row names is to hash it myself. More typing to get it going, but does the job.

namespace EigenRCNames
{
// The key in my case is a string, but it could be a tuple
//typedef std::tuple<std::string, std::string> rc_key_t;
typedef std::string rc_key_t;

struct key_hash : public std::unary_function<currency_key_t, std::size_t>
{
    std::size_t operator()(const rc_key_t& k) const
    {
        std::hash<std::string> hash_fn;

        return hash_fn(k);
    }
};

struct key_equal : public std::binary_function<rc_key_t, rc_key_t, bool>
{
    bool operator()(c rc_key_t& v0, const  rc_key_t& v1) const
    {
        return (v0 == v1);
    }
};

struct data
{
    int row;
    int column;

    inline bool operator ==(data d)
    {
       if (d.row == row && d.column == column)
          return true;
       else
          return false;
    }

    friend std::ostream& operator << (std::ostream& os, const data& rhs)    //Overloaded operator for '<<'
    {                                                                       //for struct output
        os  << rhs.row << ", "
            << rhs.column;

        return os;
    }
};

typedef std::unordered_map<const  rc_key_t, data, key_hash, key_equal> map_t;
//                                                     ^ this is our custom hash

}

Then,

//Row STRAWBERRY and Column BANANA maps to {0,0}
static std::string STRAWBERRYBANANA = "STRAWBERRY-BANANA";
data dSTRAWBERRYBANANA = {0, 0};

static map_t m;

m[STRAWBERRYBANANA] = dSTRAWBERRYBANANA;

And then searching by key "STRAWBERRY-BANANA" or value {0, 0} is straigthforward.