c++ - How to order a set< pair< pair<int, int>, double > > for the second value "double"? -

i super new in c++ , struggling this: want organize second component of set:

set< pair <pair<int, int>, double > > map int n_t = 10, n_r = 10; (unsigned int i_t = 0; i_t < n_t; i_t++ )  {  for(unsigned int i_r = 0; i_r < n_r; i_r++ )   {    double_t dr = i_t*i_r ;    map.insert( make_pair(make_pair(i_r, i_t) ,dr));    }  } 

and want organice second component. have try , dont know how to it:

sort(map.begin(), map.end(), [](const pair<pair<int,int> &x, double>,const pair<pair<int,int>, double> &y) {   return x.second < y.second;  }); 

thanks!!

if wish sort according .second element of pair, why not placing double in front of pair<int,int>? sorting orders pairs first element second element, instead of

set< pair <pair<int, int>, double > > map 

you use

set< pair <double, pair<int, int> > > map 

also suggest not using keywords variable names (map in-built data structure in c++)