Thanks. I have problems compiling it. ../Test.cpp:74: error: invalid initialization of non-const reference of type 'std::_Rb_tree_iterator<std::pair<const std::pair<int, int>, std::basic_string<char, std::char_traits<char>, std::allocator<char> >

...

&' from a temporary of type 'std::_Rb_tree_iterator<std::pair<const std::pair<int, int>, std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >' ../Test.cpp:71: warning: unused variable 'itr'

Here is my code: main() { typedef pair<int, int> intPair; typedef map < intPair, string> pairMapString; int x = 3; pairMapString myMap; pairMapString::iterator& itr = find_if(myMap.begin(), myMap.end(), bind(&intPair::first, bind(&pairMapString::value_type::first, _1)) == x); } On 2/22/06, Kevin Heifner <heifner_k@ociweb.com> wrote:

Meryl Silverburgh wrote:

...

I have a map with key is a pair: typedef map < pair<int, int>, string> pairMapString;

pair<int, int> key(1,3); map[key] = "one";

How can I create a binary function using boost lamba which check the first value of the pair of the key of the map?

void add(pairMapString;& myMap, int x) {

iterator& itr = find_if(myMap.begin(), myMap.end(), bind(equal_to < int >(), bind(&BlockDataPairMap::value_type::first::value_type::first, _1 ) , x) );

using namespace std; using namespace boost::lambda;

typedef pair<int, int> intPair; typedef map < intPair, string> pairMapString;

void add(pairMapString& myMap, int x) { pairMapString::iterator& itr = find_if(myMap.begin(), myMap.end(), bind(&intPair::first, bind(&pairMapString::value_type::first, _1)) == x); }

KevinH -- Kevin Heifner heifner @ ociweb.com http://heifner.blogspot.com Object Computing, Inc. (OCI) www.ociweb.com _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

...

template <class T> void keySet(T& aMap, vector<int>& keySet) { transform( aMap.begin(), aMap.end(), back_inserter(keySet), bind(&T::value_type::first, _1) );

}

here is the error: g++ -O0 -g3 -Wall -c -fmessage-length=0 -oBlockGrouper.o ../BlockGrouper.cpp ../Utils.h: In function 'void keySet(T&, std::vector<int, std::allocator<int> >&)': ../Utils.h:149: error: '_1' was not declared in this scope

Based on your errors it looks like _1 is not declared in the scope. Did you miss adding these: #include <boost/lambda/lambda.hpp> using boost::lambda::_1; -- Nitin Motgi

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-- Nitin Motgi

On 2/23/06, yinglcs2@yahoo.com <yinglcs2@yahoo.com> wrote:

Thanks. I add the import and namespace, but I still get the same arror:

../Utils.h: In function 'void keySet(T&, std::vector<int, std::allocator<int> >&)': ../Utils.h:175: error: use of '_1' is ambiguous /usr/include/boost/lambda/core.hpp:69: error: first declared as 'const boost::lambda::placeholder1_type& boost::lambda::<unnamed>::_1' here

--- nitin motgi <nitin.motgi@gmail.com> wrote:

<snip> Post a complete sample - that looks like you might have included boost/lambda/bind.hpp and boost/bind.hpp Stuart Dootson

I am not sure how low_bound() will work. My understanding is it only return the ** first ** instance. but I am looking for ** all instances ** which fit the condition (i.e. the first value of the key pair matches the input parameter). --- Peter Dimov <pdimov@mmltd.net> wrote:

Meryl Silverburgh wrote:

...

I have a map with key is a pair: typedef map < pair<int, int>, string> pairMapString;

pair<int, int> key(1,3); map[key] = "one";

How can I create a binary function using boost lamba which check the first value of the pair of the key of the map?

void add(pairMapString;& myMap, int x) {

iterator& itr = find_if(myMap.begin(), myMap.end(), bind(equal_to < int >(),

bind(&BlockDataPairMap::value_type::first::value_type::first,

_1 ) ,

...

x) );

myMap.lower_bound( make_pair( x, INT_MIN ) ) should give you what you need in logarithmic time, if I'm not mistaken.

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Thanks. I would like to use your suggestion (since it is simpler/cleaner). however, you said 'you just need to proceed from the iterator lower_bound returns until you hit an element with .first != x (or end()). ' How can I find the element with .first != x? I try using end(), but it does not work. it copies evething from (.fires == x) to the end of the list. --- Peter Dimov <pdimov@mmltd.net> wrote:

yinglcs2@yahoo.com wrote:

...

I am not sure how low_bound() will work. My understanding is it only return the ** first ** instance.

But so does find_if.

...

but I am looking for ** all instances ** which fit the condition (i.e. the first value of the key pair matches the input parameter).

Since a map is sorted by its key, you just need to proceed from the iterator lower_bound returns until you hit an element with .first != x (or end()). Anyway, ...

...

...

...

iterator& itr = find_if(myMap.begin(),

... you need to omit the reference here.

iterator itr = find_if( ...

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