Weighted Random¶ ↑

Weighted randomization extension for ActiveRecord.

Gives ability to get weighted random record from particular database relation.

gem 'weighted_random'

Generate model with weight and cumulative_weight integer attributes:

rails g model your_model [your_attributes] weight:integer cumulative_weight:integer

Or add these two attributes into migration of existing model:

create_table :your_table, do |t|
  t.integer :weight
  t.integer :cumulative_weight
end

It is a good idea to add index on cumulative_weight attribute:

add_index :your_table, :cumulative_weight

Based on Benchmark.bmbm times, it makes creating of records 2 times faster and getting a random record 11 times faster!

Finally, load weighted randomization stuff into desired model and set accessibillity of weight attribute:

class YourModel < ActiveRecord::Base
  weighted_randomizable
  attr_accessible :weight
end

Just create records, each must contain weight value:

LastName.create [
  {:name => 'Smith',    :weight => 10},
  {:name => 'Johnson',  :weight => 8},
  {:name => 'Williams', :weight => 7},
  {:name => 'Jones',    :weight => 6},
  {:name => 'Brown',    :weight => 6},
  {:name => 'Davis',    :weight => 5},
  {:name => 'Miller',   :weight => 4},
  {:name => 'Wilson',   :weight => 3}
]

It automatically sets cumulative_weight attribute for each record.

Here is an example of importing data from CSV file:

db/seeds/last_names.csv:

name,weight
Smith,10
Johnson,8
Williams,7
Jones,6
Brown,6
Davis,5
Miller,4
Wilson,3

db/seeds.rb:

LastName.create(
  CSV.table(File.expand_path('seeds/last_names.csv', File.dirname(__FILE__))).collect(&:to_hash)
)

To get weighed random record simply run:

LastName.weighted_rand

Demonstration:

10.times { puts LastName.weighted_rand.name }
Johnson
Brown
Johnson
Smith
Smith
Jones
Smith
Williams
Miller
Jones

Szymon Przybył (github.com/apocalyptiq)