Re: [Boost-users] Iterator over values of std::map<K, V>

I'll copy my code tomorrow, I'm not at my workstation right now. However, I'm pretty sure that adapting the iterator is faster than copying the values/keys into a collection in advance. John On 11/30/07, chun ping wang wrote:

hey i am curious on the actual code you written. Cause i want to know if doing that is faster than copying an item to a container and like iterate over that.

template < class T, class U, template class CONT > CONT<T> getKeys(const boost::unordered_map& data) { CONT<T> retCont; typedef typename boost::unordered_map::value_type value_type; BOOST_FOREACH(value_type val, data) { retCont.push_back(val.first); } return retCont; }

Note i am using keys instead of value but concept is the same. On Nov 30, 2007 1:59 AM, John Kiopela wrote:

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Thanks a lot both. Transform Iterator did the trick.

Kind regards,

John

On Nov 29, 2007 9:04 PM, Niels Aan de Brugh wrote:

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On 2007-11-29, John Kiopela wrote:

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I have been browsing through the docs, but I couldn't find anything

useful.

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Does Boost have a std::map::iterator adaptor which iterates over the values of the map only.

What about using a boost::transform_iterator<>? Docs at:

http://boost.org/libs/iterator/doc/transform_iterator.html

You'd have to supply it with a function object that returns the 'second' member variable of the pair, e.g.

struct get_pair_value { template< typename K, typename V > V operator()( std::pair< K, V > const& pr ) { return pr.second; } };

Or you could use Boost.Lambda.

N.

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