C# Dictionary Add/Set in one call for performance reasons

Question

In a Dictionary<struct,int>: is it possible to Add/Set in one call?

So is it possible to do the code below in only one lookup per entry?

_KeyToPoints = new Dictionary<Key,int>();

foreach ( var entry in billionEntries )
{
    int originalValue;

    // first lookup
    _KeyToPoints.TryGetValue(entry.Key, out originalValue);

    // second lookup
    _KeyToPoints[key] = originalValue + points;    
}

This is done in a very tight loop over a huge amount of data, so all performance matters.

Or is there a better suitable data structure?

Answer 1

Yes, there is a way to do this, but it has a downside. Consider this class:

class Ref<T>
{
    public T Value;
}

You can use a Dictionary<K, Ref<int>> dict and then do this:

Ref<int> count;
if (!dict.TryGetValue(key, out count))
{
    count = new Ref<int> { Value = 0 };
    dict[key] = count;
}
count.Value += points;

The downside is that now you have an additional heap object per entry in your dictionary. Depending on your situation, this may or may not be acceptable.