Why unordered_set

I'm trying to get a list of iterators to erase from a string. I wanted to do it with unsorted_set because access time is constant and I'll be doing lookup often but it gives me a compile error. unordered_set<string::iterator> to_erase However if i try to define vector<string::iterator> to_erase it works.

But then when I try to do:

find(to_erase.begin(),to_erase.end(),it)

It doesn't work