CODEWITHSUNDEEP
algorithmrating
Joe.webdev
Joe.webdev

Reputation: 3

Comparative rating algorithm

UseCase: Assume that rating of object is from 1 to 5 stars. It is already 50 votes with avarage rating 4.1. When user make a vote(1-5stars), whe need to recalculate rating.

How to implement that logic? Problem is we don't know the value of every vote, only current rating and total votes.

Upvotes: 0

Views: 142

Answers (3)

SplinterOfChaos
SplinterOfChaos

Reputation: 489

Assuming:

f = (1+2+3)/3 = 6/3 = 2
  = (2+2+2)/3 = 6/3 = 2

We know that f=g. If we know the current rating is 2, and the total number of votes is 3, 2*3=6 as the sum of all votes. Let's add 4 to our average like so:

f = 6/3
f' = (6+4)/4 = 2.5

Upvotes: 0

Juraj Blaho
Juraj Blaho

Reputation: 13471

newRating = (oldRating * oldCount + currentVote) / (oldCount + 1)

Upvotes: 4

SilverbackNet
SilverbackNet

Reputation: 2074

Well, basic arithmetic tells us that (50 * 4.1 + newvote) / 51 is the same as the average of all votes. You'll end up with roundoff errors if you do it repeatedly, and after a certain number of votes it's not even worth bothering with averaging in a single vote, but the basic formula is sound.

Upvotes: 0

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