Question

I’m trying to develop a rating system for an application I’m working on. Basically app allows you to rate an object from 1 to 5(represented by stars). But I of course know that keeping a rating count and adding the rating the number itself is not feasible.

So the first thing that came up in my mind was dividing the received rating by the total ratings given. Like if the object has received the rating 2 from a user and if the number of times that object has been rated is 100 maybe adding the 2/100. However I believe this method is not good enough since 1)A naive approach 2) In order for me to get the number of times that object has been rated I have to do a look up on db which might end up having time complexity O(n)

So I was wondering what alternative and possibly better ways to approach this problem?

Answer 1

You can keep in DB 2 additional values – number of times it was rated and total sum of all ratings. This way to update object’s rating you need only to:

1. Add new rating to total sum.
2. Divide total sum by total times it was rated.