a map question

Hi,all, I have the following map:

map<int, vector<MSXML2::IXMLDOMNodePtr>> nodes;

which uses int as the keys (starting from 1), and vector<MSXML2::IXMLDOMNodePtr> as the mapped values. Now I want to do some calculation/comparison between the vector with index value 1 and the rest of the vectors.

for each vector i except the first vector in the map do
    calFunc(vector_1, vector_i);
    // some other work

so how may I approach that?

cheers