Rails query random records using weights

Question

let say I have a model Product

There are products

id | title   | weight (integer)
1  | Sugar   | 1
2  | Salt    | 1
3  | Pepper  | 2
4  | Coke    | 5

So, I want to get few (lets say 2) random products using weights.

Product.limit(2).rand_with_weights # =>
# The probability of coke is in array is 5x times bigger than salt or sugar and 2.5x times bigger than pepper
# The probability of pepper is in array is 2x times bigger than salt or sugar
# The probability of salt or sugar in array is equal

How can I make this query?

This might be really helpful: http://stackoverflow.com/a/13040717/312907 although what @Pavan says seems quite reasonable, be careful however that it's mentioned to give wrong distribution as stated in one of the comments — Francesco Belladonna, Jul 18 '15 at 18:02

MHL · Answer 1 · 2019-07-25T06:01:12.507

2

According to Efraimidis & Spirakis's paper: https://utopia.duth.gr/~pefraimi/research/data/2007EncOfAlg.pdf

If you are using postgres:

Product.order("RANDOM() ^ (1.0 / weight) DESC").limit(2)

proof of concept: http://sqlfiddle.com/#!17/474d2/4/0

As you can see the distribution is as expected

edited Jul 25 '19 at 06:01

answered Jul 25 '19 at 05:25

MHL

81
6

Rails query random records using weights

1 Answers1