CODEWITHSUNDEEP
c++vectorstl
Daniel Del Core
Daniel Del Core

Reputation: 3221

Find pair by key within a vector of pairs

I want to call the find function on a vector of pairs. At the time the find function is called I only have the key to search by.

My understanding is that I need to pass a function into find as an argument to do the comparison for me but I can't find a proper example.

The reason I'm sorting the pairs within a vector opposed to a map container is because I want to be able to sort the pairs by value after the population process.

    vector< pair<string, int> > sortList;
    vector< pair<string, int> >::iterator it;

    for(int i=0; i < Users.size(); i++)
    {
        it = find( sortList.begin(), sortList.end(), findVal(Users.userName) );

        //Item exists in map
        if( it != sortList.end())
        {
            //increment key in map
            it->second++;
        }
        //Item does not exist
        else
        {
            //Not found, insert in map
            sortList.push_back( pair<string,int>(Users.userName, 1) );
        }
    }

    //Sort the list

    //Output

The implementation on findVal is the fuzzy area for me. I'd also be open to better ways of implementing the logic.

Upvotes: 40

Views: 111142

Answers (2)

cigien
cigien

Reputation: 60218

From C++20, you can use ranges to write:

auto it = std::ranges::find(sortList, Users.userName, 
                            &std::pair<std::string, int>::first);

which is much easier to read. The 3rd argument is a projection, i.e. it says to look only at the first member of every pair in the vector, when comparing it against the second argument.

Upvotes: 11

BlackMamba
BlackMamba

Reputation: 10254

you don't need use find, please use find_if, this is the link:http://www.cplusplus.com/reference/algorithm/find_if/

auto it = std::find_if( sortList.begin(), sortList.end(),
    [&User](const std::pair<std::string, int>& element){ return element.first == User.name;} );

If you are using C++ standard before C++11, later, you'll need a function instead of a lambda:

bool isEqual(const std::pair<std::string, int>& element)
{
    return element.first ==  User.name;
}
it = std::find_if( sortList.begin(), sortList.end(), isEqual );

Upvotes: 63

Related Questions