Array Consistent Sample

Calling Array#consistent_sample works like Array#sample, but produces consistent output if:

  • the Array's contents are unchanged
  • the arguments to #consistent_sample are the same


Supports Ruby 1.8.7 and 1.9.3+. However, for Ruby 1.8.7, you will need the backports gem installed so that Array#sample and Random will be available.

What problem does this solve?

This gem was built to spread load over background job servers for tasks that don't need to run on every background server. Single or multiple background server names can be consistently sampled from a set of currently running background servers, with job names passed to vary the results and spread load. If, hypothetically, a previously selected background server goes away, a different one is consistently selected from the altered set of background servers.


people = ['Sally', 'Bob', 'Alice', 'Joe']

The same array and same arguments always gets you the same results (results may vary between Ruby versions and platforms, but should be consistent for that same Ruby and platform).

# => ["Sally"]
# => ["Sally"]

You can pass an optional second parameter to vary the sample.

people.consistent_sample(1, 'Mow the lawn')
# => ["Alice"]

people.consistent_sample(2, 'Sort recycling')
# => ["Sally", "Alice"]

people.consistent_sample(2, 'Wash the dishes')
# => ["Bob", "Joe"]

people.consistent_sample(3, 'Bring about world peace')
# => ["Bob", "Alice", "Joe"]