Re: [Boost-users] Re: Key iterators

18 Nov 2004


      On Thu, 18 Nov 2004 15:21:06 -0700, Chris Goller
<cgoller@magpiesystems.com> wrote:
...
David-
Thanks.
Upon reading my poorly phrased email I realized this:
I want unique keys so that if the data looks like this:
key         value
3            1
1            2
1            4
4            3
5            5
5            9
So, what I would like to do is to a print each value for a particular
key in such a way:
key:         value:
1----
    |------2
    |------4
3----
    |------1
4----
    |------3
5----
    |------5
    |------9
Or, for example, if I had a list of directories as keys and and files
are their values then for each directory I could print out the file.
Right now, I do this:
for (multimap<string, string>::iterator dir = filesystem.begin(); i !=
filesystem.end())
{
    pair<multimap<string, string>::iterator, multimap<string,
string>::iterator> bounds;
    bounds = filesystem.equal_range(dir->first);
    cout << dir->first << "----" << endl;
    for (multimap<string, string>::iterator file = bounds.first;  file
!= bounds.second; file++)
    {
       cout << "    |------" << file->second  << endl;
    }
    // Moves the directory iterator to the next directory key.
    dir = file;
}
So, I'm trying to get better at using iterators much smarter.  I would
like to make this code much more concise.
I figured that if I could jump from key to key I write the above code
much cleaner.
You can use multimap::upper_bound instead of iter++ to help navigate
the unique key space:

using namespace std;
using namespace boost::assign;

typedef multimap<int, int> mymap;
mymap m = map_list_of (1,1)(1,2)(1,3)(2,1)(2,2)(2,3)(3,1)(3,2)(4,9)(5,10);

for (mymap::const_iterator i = m.begin (); i != m.end (); i =
m.upper_bound (i->first))
   cout << i->first << endl;

outputs
1
2
3
4
5


-- 
Caleb Epstein
caleb dot epstein at gmail dot com