Should I use a Dictionary for collections with 10 items or less, or is there a better alternative?

I have a list of objects and I need to find an object as quickly as possible (by it's name property). What data-structure should I use? I know I can use a Dictionary, but there wont ever be more than 10 items 开发者_如何转开发in the list, and if I remember correctly the dictionary is implemented as an array if the collection contains 10 items or less.

Thanks.

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MSDN recommends the ListDictionary for collections with 10 items or less:

This is a simple implementation of IDictionary using a singly linked list. It is smaller and faster than a Hashtable if the number of elements is 10 or less. This should not be used if performance is important for large numbers of elements.

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You may want to consider the System.Collections.Specialized.ListDictionary if you are certain there will be less than ten items.

Also consider the System.Collections.Specialized.HybridDictionary which switches behaviour (with a small overhead) should the size increase above a threshold, handy if your assumption is wrong.

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Since you want fastest possible lookup by a property you should use Dictionary<Key, Value>. The size doesn't hurt you if you want fast lookup. It's not that a Dictionary<Key, Value> of just 10 items or less is taking up a ton of memory. Dictionary<Key, Value> has a constructor that takes an int to set the capacity.

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Why not just use a Hashtable? It's in the System.Collections namespace.

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For your case, KeyedCollection<TKey, TItem> will do. It is a hybrid structure, the constructor takes a parameter to denote from what size onward the structure should switch from linear list to a hash based lookup. And yes it is generic.

One downside is it is an abstract class, so you will have to derive one yourself.

public class KeyedCollection<TKey, TItem> : System.Collections.ObjectModel.KeyedCollection<TKey, TItem>
{
    private readonly Func<TItem, TKey> m_keySelector;

    public KeyedCollection(Func<TItem, TKey> keySelector)
        : this(keySelector, null)
    {
    }

    public KeyedCollection(Func<TItem, TKey> keySelector, IEqualityComparer<TKey> comparer)
        : this(keySelector, comparer, 10)
    {
    }

    public KeyedCollection(Func<TItem, TKey> keySelector, IEqualityComparer<TKey> comparer, int dictionaryCreationThreshold)
        : base(comparer, dictionaryCreationThreshold)
    {
        m_keySelector = keySelector;
    }

    protected override TKey GetKeyForItem(TItem item)
    {
        return m_keySelector(item);
    }
}

Then you could call it:

var foo = new KeyedCollection<Foo, string>(f => f.Name, null, 10);