Consistent splitting using hashing and modulo

hashing_example.rb

require 'zlib'

six_items = ["item_1", "item_2", "item_3", "item_4", "item_5", "item_6"]
ten_items = ["item_1", "item_2", "item_3", "item_4", "item_5", "item_6", "item_7", "item_8", "item_9", "item_10"]

chunks = 3 # should be set once and stay constant to preserve item<=>feed stickiness

six_items.each { |item_id| puts "#{item_id} goes to feed ##{Zlib.crc32(item_id) % chunks}" }
ten_items.each { |item_id| puts "#{item_id} goes to feed ##{Zlib.crc32(item_id) % chunks}" }
ten_items.reverse.each { |item_id| puts "#{item_id} goes to feed ##{Zlib.crc32(item_id) % chunks}" }

# -----------------------------------
irb(main):008:0> six_items.each { |item_id| puts "#{item_id} goes to feed ##{Zlib.crc32(item_id) % chunks}" }
item_1 goes to feed #0
item_2 goes to feed #1
item_3 goes to feed #0
item_4 goes to feed #1
item_5 goes to feed #2
item_6 goes to feed #0
=> ["item_1", "item_2", "item_3", "item_4", "item_5", "item_6"]

# order stays the same for larger number of items
irb(main):009:0> ten_items.each { |item_id| puts "#{item_id} goes to feed ##{Zlib.crc32(item_id) % chunks}" }
item_1 goes to feed #0
item_2 goes to feed #1
item_3 goes to feed #0
item_4 goes to feed #1
item_5 goes to feed #2
item_6 goes to feed #0
item_7 goes to feed #0
item_8 goes to feed #1
item_9 goes to feed #0
item_10 goes to feed #2
=> ["item_1", "item_2", "item_3", "item_4", "item_5", "item_6", "item_7", "item_8", "item_9", "item_10"]

# order stays the same for reversed list of items
irb(main):010:0> ten_items.reverse.each { |item_id| puts "#{item_id} goes to feed ##{Zlib.crc32(item_id) % chunks}" }
item_10 goes to feed #2
item_9 goes to feed #0
item_8 goes to feed #1
item_7 goes to feed #0
item_6 goes to feed #0
item_5 goes to feed #2
item_4 goes to feed #1
item_3 goes to feed #0
item_2 goes to feed #1
item_1 goes to feed #0
=> ["item_10", "item_9", "item_8", "item_7", "item_6", "item_5", "item_4", "item_3", "item_2", "item_1"]