Re: some combination of std::distance/std::max_element ( ? )

From:
"ma740988" <ma740988@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
28 Apr 2006 09:26:13 -0400
Message-ID:
<1146181635.010970.266860@i39g2000cwa.googlegroups.com>
Carl Barron wrote:

[.....]

    Where For1 and For2 are forward iterators [faster if For1 is
actually a random access iterator] and Out is an output iterator.
and For1::value_type has an operator < .

This will work with any STL sequence containers.

Awesome. Often desirable for what I'm doing.

    std::vector<int> sizes{3,3};
    std::vector<double> data;
       // place the six values in data.
    std::vector<double> max_of_zone;
    max_zones(data.begin(),data.end(),sizes.begin(),sizes.end(),
       std::ostream_iterator<double>(std::cout,",'));

   will print the max's as a comma separated list.

     Isn't that shorter and easier to read??


Incredible.

How would my approach below rank in the shorter and easier to read
category?

At issue:
Compare the keys @ element and element+ 1 in a map against some
threshold. If condition is met. Compare the values. Remove the
lower..

typedef std::map< int , double > MMAP;
void run_it ( MMAP& m, int num )
{
  MMAP::iterator it1 = m.begin();
  MMAP::iterator it2 = m.begin();
  if (it2 != m.end()) ++it2;
  while (it1 != m.end() && it2 != m.end())
  {
    bool success ( false );
   // if difference between Key and Key + 1 < num
   //std::cout << it1->first << " " ;
  //std::cout << it2->first << std::endl;

    if ( ( it2->first - it1->first ) < num )
    {
      if ( it1->second < it2->second )
      {
        m.erase(it1);
        it1 = ++it2;
      }
      else
      {
        m.erase(it2++);
        it1 = it2;
        if (it2 != m.end()) ++it2;
      }
      success = true;
    }
    // increment -
    if (it2 != m.end()) ++it2;
    if (!success )
    {
      ++it1;
    }
  }
}
int main()
{
  MMAP mp;
  mp.insert( std::make_pair ( 0 , 3.2 ) );
  mp.insert( std::make_pair ( 1 , 9.2 ) );
  mp.insert( std::make_pair ( 3 , 2.8 ) );
  mp.insert( std::make_pair ( 4 , 4.2 ) );
  int num ( 3 ) ;
  run_it ( mp, num ) ;

  MMAP::iterator end = mp.end();
  for ( MMAP::iterator it = mp.begin(); it != end; ++it )
    std::cout << " ( " << it->first << ", "
                << it->second << " ) "
        << std::endl;
}
Curious to see ( more importantly learn ) how you'd approach this.

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