When to use a HashTable

Question

In C#, I find myself using a List, IList or IEnumerable 99% of the time. Is there a case when it would be b

Answer 1

You use a hashtable (dictionary) when you want fast look up access to an item based on a key.

If you are using List, IList or IEnumerable generally this means that you are looping over data (well in the case of IEnumerable it definitely means that), and a hashtable isn't going to net you anything. Now if you were looking up a value in one list and using that to access data in another list, that would a little different. For example:

1. Find position in list of Item foo.
2. Position in list for foo corresponds to position in another list which contains Foo_Value.
3. Access position in seconds list to get Foo_Value.

Here is a link describing the different datatypes.

Another link.