list with non-unique index
<p>I've always thought the any index should be unique, but I think it's not true at least for SQL Server as shown in the following post:</p>

<p><a href="http://stackoverflow.com/questions/4332982/do-clustered-indexes-have-to-be-unique">Do clustered indexes have to be unique?</a></p>

<p>Recently I had to store a very amount of data within a collection and thought of using a dictionary for it's the fastest collection to get an object by index. But my collection would have to allow duplicated keys. But in fact duplicated keys would not be a problem since any of the object returned would be meet the requirements (The objects are not exactly unique, but the keys would be).</p>

<p>Some more research led me to the following post:</p>

<p><a href="http://stackoverflow.com/questions/4598826/c-sharp-hashset-contains-non-unique-objects">C# Hashset Contains Non-Unique Objects</a></p>

<p>Which shows a way to get a HashSet with "duplicated keys". His problem would be my solution but I wonder if there's any other way that I can have a list with duplicated keys which allows me to search very fast without having to do any workaround the get this done.</p>
