Sorting a std::vector<std::pair<std::string,bool>> by the string?

Question

How can I sort this vector by comparing the pair.first which is an std::string? (without providing a static compare function, nor use boost).

Answer 1

std::vector<std::pair<std::string, bool> > v;
std::sort(v.begin(), v.end());

std::pair overloads operator< to sort first by the first element then by the second element. Thus, if you just sort the vector using the default sort ordering (operator<), you'll get your desired ordering.

Answer 2

I really like James' answer, but there's one other option you might want to consider - just funnel everything into a std::map:

std::map<std::string, bool> myMap(v.begin(), v.end());

Or, if you have duplicate strings, a std::multimap:

std::multimap<std::string, bool> myMultiMap(v.begin(), v.end());

This does have the added advantage that if you then need to add or remove new key/value pairs, you can do so in O(lg n), as opposed to O(n) for the sorted vector.

If you really must use a vector, then go with James' answer. However, if you have a vector of pairs, there's a good chance that you really want a std::map.

Answer 3

You can use a custom comparator to order on the pairs' .first only.

sort(begin, end,
     compose2(less<string>(),
              select1st<pair<string, bool> >(),
              select1st<pair<string, bool> >()));

Answer 4

Answer to "duplicate question" of this: link: Sort a vector of pairs by first element then by second element of the pair in C++?

bool cmp(const pair<int,int>&x,const pair<int,int>y){
if(x.first==y.first){
   return(x.second<y.second);
}
return(x.first<y.first);
}

array of pairs before:
5 2
4 2
8 2
8 3
8 1
array of pairs after:
4 2
5 2
8 1
8 2
8 3