gistfile1.rb

class MergeColumn
  def initialize(array)
    @array = array
    @index = 0
  end
  
  def value
    @array[@index]
  end
  
  def empty?
    @index > @array.size - 1
  end
  
  def pop
    @index += 1
    @array[@index - 1]
  end
  
  def <=>(o)
    self.value <=> o.value
  end
end

class Array
  def merge_sort(n = nil)
    columns = self.collect { |e| MergeColumn.new(e) }
    result = []
    while !columns.empty? && (n.nil? || n > result.size)
      col = columns.shift
      result << col.pop
      unless col.empty?
        columns.push(col) 
        # this part could be an insertion sort instead of a full resort every time
        columns.sort!
      end
    end
    result
  end
end



unsorted = (1..100).to_a.inject({}) do |h, k| 
  h[k] = []
  # 500.times { h[k] << {"created_at" => Time.at(rand(Time.now.to_i))} }
  # h[k].sort! {|a, b| a["created_at"] <=> b["created_at"]}
  500.times { h[k] << rand(Time.now.to_i)  }
  h[k].sort!
  h 
end
require 'benchmark'
flat = unsorted.values.flatten
vals = unsorted.values
# puts unsorted.values.merge_sort(10)
# puts
# puts unsorted.values.flatten.sort[0, 10]


Benchmark.bmbm do |x|
  x.report("merge") { 100.times { unsorted.values.merge_sort(10) } }
  x.report("ruby sort") { 100.times { flat.sort[0,10] } }
end