Re: std::transform for std::map

it doesn't seem to be possible to use transform for maps.

#include <algorithm>
#include <map>
#include <iterator>
#include <vector>
#include <iostream>

using namespace std;

int doit(int w) {
    return w+1;
}

int main() {
    map<int,int> m;
    vector<int> v;
    m[0]=42;
    v.push_back(42);
    //transform(m.begin(),m.end(),m.begin(),doit); (*)
    transform(v.begin(),v.end(),v.begin(),doit);
    copy(v.begin(),v.end(),ostream_iterator<int>(cout," "));
    cout<<endl;
}

I understand syntactically why the line (*) does not compile.
But conceptually is doesn't make much sense (IMHO) to not be
able to use maps in std::tranform. Even changing doit to

pair<int, int> doit(pair<int, int> w) {
    pair<int,int> result(w);
    w.second++;
    return result;
}

doesn't help. What would be the right way to do it?