Question

I’ve got a list of items. Users can occasionally select them. Now I want to order the items by their popularity. What’s a good weighting function for that?

Constraints:

• The weight should be in [0,1)
• Recursive calculation is prefered (not required)
• Newer events must have more influence than old ones.
• I’d favor approved functions. As I’ve developped something like this once and it worked not as expected.

Answer 1

If you have a counter of votes per item, you can use a ‘fading constant’ in order to make older votes “fade away” with time. Something like:

Nvotes(i) = IsClicked(i) + Nvotes(i) * Kfade

where: 0 < Kfade < 1

Thus, whenever a new click is intercepted, all counters are advanced where only the selected item is incremented by 1.

EDIT: Since the total is less than 1, you may want to normalize Nvotes by the total number of clicks so far.