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Print all the occurrences of a word in a MAP

Amiplus (168)



Hello everyone,



i'm trying to count how many paired words are present in a map as follow:
 
 
map<string, string>::iterator it = dictionary.find(wordToSearch);


I populated the dictionary this way:

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dictionary.insert(make_pair("PLUTO", "MICKEY"));
dictionary.insert(make_pair("PLUTO", "DONALD"));


why with the following code i can output only the first occurrence?

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    for (it = dictionary.begin();
            it != dictionary.end(); ++it)
    {
        if (it->first==wordToSearch) {
            cout << it->first << "\t" << it->second << endl;
        }
    }


thank you very much
Last edited on
JLBorges (13770)
In std:map the keys are unique: there can be only one key value pair for a particular key.
Use std::multi_map instead of std:map if multiple entries with the same key is required.

For example:
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#include <iostream>
#include <map>
#include <string>

int main()
{
    std::multimap<std::string,std::string> mmap { { "PLUTO", "MICKEY" }, { "PLUTO", "DONALD" } } ;
    mmap.emplace( "PLUTO", "HUEY" ) ;
    // etc.

    const auto pair = mmap.equal_range( "PLUTO" ) ;
    for( auto iter = pair.first ; iter != pair.second ; ++iter )
        std::cout << iter->first << ' ' << iter->second << '\n' ;

    std::cout << '\n' ;

    // or C++ 17:
    const auto [ begin, end ] = mmap.equal_range( "PLUTO" ) ;
    for( auto iter = begin ; iter != end ; ++iter )
    {
        const auto& [ key, value ] = *iter ;
        std::cout << key << ' ' << value << '\n' ;
    }
}

http://coliru.stacked-crooked.com/a/ba180b20683db751
Amiplus (168)
Thank you.

I thought this was possible.

Have to modify a little the code, sice the dicttionary rely on a map

Kind regards
Last edited on
Amiplus (168)
@JLBorges

looking at the code you posted, is not possible to as follow:
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std::multimap<std::string,std::string> mmap { { "PLUTO", "A DOG", "CUTE DOG", "THIS DOG BELONGS TO MICKEY" }, { "PLUTO", "DONALD" } } ;
    mmap.emplace( "PLUTO", "HUEY" ) ;
Last edited on
JLBorges (13770)
This is possible:

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#include <iostream>
#include <map>
#include <string>

template < typename K, typename V, typename KK, typename VV >
void insert_all( std::multimap<K,V>& mmap, const KK& key, std::initializer_list<VV> values )
{ for( auto v : values ) mmap.emplace( key, v ) ; }

int main()
{
    std::multimap<std::string,std::string> mmap { { "PLUTO", "MICKEY" }, { "PLUTO", "DONALD" } } ;
    mmap.emplace( "PLUTO", "HUEY" ) ;
    insert_all( mmap, "PLUTO", { "A DOG", "CUTE DOG", "THIS DOG BELONGS TO MICKEY" } ) ;
    insert_all( mmap, "Neptune", { "Sylvester", "Bugs", "Daffy", "Tweety", "Wile E Coyote" } ) ;
    // etc.

    const auto pair = mmap.equal_range( "PLUTO" ) ;
    for( auto iter = pair.first ; iter != pair.second ; ++iter )
        std::cout << iter->first << ' ' << iter->second << '\n' ;

    std::cout << '\n' ;

    // or C++ 17:
    const auto [ begin, end ] = mmap.equal_range( "Neptune" ) ;
    for( auto iter = begin ; iter != end ; ++iter )
    {
        const auto& [ key, value ] = *iter ;
        std::cout << key << ' ' << value << '\n' ;
    }
}

http://coliru.stacked-crooked.com/a/7e5ad4053ea11ea5
Amiplus (168)
Thank you JLB,

In that case i can have multiple keys, i.e. "PLUTO", with multiple associated strings?

Cool.

there's a limit to the number of arguments for a key?

moreover, it's possibile to access directly the second, third.... elements, as well as counting the number of elements for each key?

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const auto pair = mmap.equal_range( "PLUTO" ) ;
    for( auto iter = pair.first ; iter != pair.second ; ++iter )
        std::cout << iter->first << ' ' << iter->second << '\n' ;

    std::cout << '\n' ;


Last edited on
JLBorges (13770)
> there's a limit to the number of arguments for a key?

No. (Other than the limitation of available memory.)


> possible to access directly the second, third.... elements,
> as well as counting the number of elements for each key?

Strongly consider using a map where the mapped value is a sequence of strings.
That is std::vector<std::string>. For instance: 

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#include <iostream>
#include <map>
#include <string>
#include <vector>
#include <iomanip>

template < typename T, typename U >
void push_back_all( std::vector<T>& vec, std::initializer_list<U> values )
{ vec.insert( vec.end(), values.begin(), values.end() ) ; }

int main()
{
    std::map< std::string, std::vector<std::string> > map
    {
        { "PLUTO", { "A DOG", "CUTE DOG", "THIS DOG BELONGS TO MICKEY" } },
        { "Neptune", { "Sylvester", "Bugs", "Daffy", "Tweety", "Wile E Coyote" } }
    };

    push_back_all( map["PLUTO"], { "Mickey", "Donald", "Huey" } ) ;
    push_back_all( map["Jupiter"], { "d'Artagnan", "Athos", "Porthos", "Aramis" } ) ;

    for( const std::string key : { "PLUTO", "Neptune", "Jupiter", "asdfgh" } )
    {
        std::cout << "key: " << std::quoted(key) ;

        const auto iter = map.find(key) ; 

        if( iter == map.end() ) std::cout << " is not present in the map\n" ;

        else
        {
            std::cout << "  values (" << iter->second.size() << "): [ " ;
            for( const auto& value : iter->second ) std::cout << std::quoted(value) << ' ' ;
            std::cout << "]\n\n" ;
        }
    }
}

http://coliru.stacked-crooked.com/a/d076dad2b6f6d63e
Amiplus (168)
@JLB

Thank you. You rocks, dude. Lightining fast!

Strongly consider using a map where the mapped value is a sequence of strings.
That is std::vector<std::string>. For instance:


I can still use in that case more than one word with the same key?

It is possible with some trick to edit one of the string associated? Assuming i want to substitute "Huey" with "Daisy", should i erase the key and insert again?

Thank you very much


Last edited on
JLBorges (13770)
If it is one of the values in the vector, it can be directly replaced. For example,
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map["PLUTO"].back() = "Daisy" ;
map["Jupiter"][2] = "Daisy" ;
// etc.


If it the key that has to be changed, it has to be reinserted.
In C++17, we can do this without reallocation of the elements. For example:
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// Change key "PLUTO" to "Mercury"
// https://en.cppreference.com/w/cpp/container/map/extract
auto node_handle = map.extract("PLUTO") ;
node_handle.key() = "Mercury" ;
map.insert( std::move(node_handle) ) ;

Snippet: http://coliru.stacked-crooked.com/a/587d68943d183507
Amiplus (168)
Fantastic!

with c++14 you can't change the key, but you have to reallocate?


JLBorges (13770)
Yes. Something like this, to avoid copying the contents of the vector:
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// Change key "PLUTO" to "Mercury" 
auto iter = map.find("PLUTO") ;
if( iter != map.end() )
{
    auto vec = std::move( iter->second ) ;
    map.erase(iter) ;
    map.emplace( "Mercury", std::move(vec) ) ;
}

Snippet: http://coliru.stacked-crooked.com/a/6a9a538bc2f24fa7


Amiplus (168)
Thank you very much.
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