title: Efficient way to get a range of Keys from Dictionary
body: <p>I have a <code>Dictionary</code> that for most operations I just need to retrieve a single entry by key, but for a few operations I will need to work with the entries associated with a range of keys. The way that occurs to me to do this is to use <code>GetKeys</code> and a <code>FindAll</code> that will match the range I am interested in, but was wondering if someone could suggest a better method. </p>