twitter/algebird — pull request #53 by azymnis (2012-12-07 17:37:31+00:00)
Title: Add a DecayedMap class and monoid.

I need the notion of a map whose values are doubles that exponentially decay over time. Here is one way to do it.

An alternative would be to extend the DecayedValue class to accept any type of value (not just double) which implements a scalable trait that could look like this:

```scala
trait Scalable[V] {
def scale(newV: V, oldV: V, epsilon: Double): V
}
```

Let me know if you think this is ok, or if you would rather have the alternative.