特征 3:矩阵行和列名称

Eigen3: Matrix row and column names

本文关键字：特征      更新时间：2023-10-16

在R中，我可以命名矩阵的行和列：

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

如何从 c++ 为 Eigen3 矩阵提供行名和列名？

由于 Eigen 似乎不支持列名和行名，我所做的就是自己进行哈希处理。更多的打字来让它继续下去，但可以完成工作。

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
}

然后

//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;

然后按键"草莓香蕉"或值 {0， 0} 进行搜索。

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