categorize.rb

require 'benchmark'

@inventory = []
@inventory << { :cat => "one" }
@inventory << { :cat => "one" }
@inventory << { :cat => "two" }
@inventory << { :cat => "two" }

def method_one(inventory)
  inventory.inject({}) do |categories_hash, item|
    if !categories_hash.has_key?(item[:cat])
      categories_hash[item[:cat]] = []
    end
    categories_hash[item[:cat]].push(item)
    categories_hash
  end
end

def method_two(inventory)
  inventory.inject({}) do |categories, item|
    if !categories.has_key?(item[:cat])
      categories[item[:cat]] = inventory.select { |i| i[:cat] == item[:cat] }
    end
    categories
  end
end

def method_three(inventory)
  inventory.group_by { |item| item[:cat] } 
end

Benchmark.bm(7) do |x|
  x.report("method_one (1000)") { 1000.times { method_one(@inventory) }}
  x.report("method_two (1000)") { 1000.times { method_two(@inventory) }}
  x.report("method_three (1000)") { 1000.times { method_three(@inventory) }}
  puts "***************"
  x.report("method_one (10,000)") { 10000.times { method_one(@inventory) }}
  x.report("method_two (10,000)") { 10000.times { method_two(@inventory) }}
  x.report("method_three (10,000)") { 10000.times { method_three(@inventory) }}
  puts "***************"
  x.report("method_one (100,000)") { 100000.times { method_one(@inventory) }}
  x.report("method_two (100,000)") { 100000.times { method_two(@inventory) }}
  x.report("method_three (100,000)") { 100000.times { method_three(@inventory) }}
end