Better Way to Randomize (Ruby/Rails 3)

Question

I'm currently using:

@users = User.order("RANDOM()").limit(6)

to generate a list of 6 random users - however, this method takes a 1200ms toll on page load times. Is there a faster/more efficient way to call 6 random users?

Something like http://stackoverflow.com/questions/2279706/select-random-row-from-an-sqlite-table/4740561#4740561 ? — captainpete, Jun 21 '11 at 01:05
have you considered this: http://stackoverflow.com/questions/3641057/rails-select-random-record/3641112#3641112 — dexter, Jun 24 '11 at 07:05

score 1 · Accepted Answer · edited May 23 '17 at 10:26

1

I ended up using the method described here: Rails select random record

@ramc - Thank you for your comment. Load times are now much faster :)

edited May 23 '17 at 10:26

Community

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answered Jul 03 '11 at 00:54

neon

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score 0 · Answer 2 · answered Jun 24 '11 at 00:45

0

Assuming auto increment ids, starting from 0 and that User objects are never deleted, the following should be quite fast:

@users = (0..5).map { User.find(rand * User.count) }

answered Jun 24 '11 at 00:45

Redbeard

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Also, it would be faster if cache the result of User.count. Excluded for brevity & clarity. – Redbeard Jun 24 '11 at 00:47

score 0 · Answer 3 · answered Jun 24 '11 at 05:14

Have you tried using a random offset & limit?

class User < ActiveRecord::Base

  def self.random num = 1
    num.times.map { offset(rand(count)).limit(1) }
  end

end

@users = User.random(6)

I've used something similar to get single random instances from AR. You'd have to make it a bit smarter if you wanted to guarantee unique results.

score 0 · Answer 4 · answered Jul 01 '11 at 06:48

0

You could get a random Page of users instead. Consider this pagination call using Kaminari

User.order('created_at').page(rand(User.count)).per(6)

This will fire one count query and one query for the page of 6 Users

answered Jul 01 '11 at 06:48

irfn

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score -2 · Answer 5 · answered Jun 21 '11 at 21:07

-2

You could try using array shuffle instead of using mysql random as it can be slow:

@users = User.all.shuffle[0..5]

After all, a collection of ActiveRecord objects is still just an Array

answered Jun 21 '11 at 21:07

Adam Carlile

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This code is valid, but the load times are the same. :( – neon Jun 21 '11 at 21:45
This also loads the entire User collection - performance will get worse as the number of user records increases. – theTRON Jun 22 '11 at 09:03
Loading the entire collection is not something you want to do, if the database does it you will not need to fetch every rows. – Schmurfy Jun 30 '11 at 21:16

Better Way to Randomize (Ruby/Rails 3)

5 Answers5