SO #13002594 Handling array of hashes

so13002594-bm.rb

#!/usr/bin/env ruby                                                                                      

# Benchmark answers to http://stackoverflow.com/questions/13002594/handling-array-of-hashes
require 'benchmark'

A = [{"lib1"=>"30"}, {"lib2"=>"30"}, {"lib9"=>"31"}, {"lib2"=>"31"}, {"lib3"=>"31"}, {"lib1"=>"32"}, {"l\
ib2"=>"32"}, {"lib1"=>"33"}, {"lib3"=>"36"}, {"lib2"=>"36"}, {"lib1"=>"37"}]

def to_a_flat
  A.map(&:to_a).flatten(1).each_with_object({}) do |(k, v), h|
    h[k] ||= []
    h[k] << v.to_i
  end
end

def to_a_flat_construct
  Hash[A.map(&:to_a).flatten(1).group_by(&:first).map { |k, v| [k, v.map(&:last).map(&:to_i)] }]
end

def group_by_each
  result = {}
  A.group_by { |x| x.keys.first }.each_pair do |k, v|
    result[k] = v.map { |e| e.values.first.to_i }
  end
end

def group_by_each_construct
  Hash[A.group_by { |x| x.keys[0] }.map { |k, v| [k, v.map { |e| e.values[0].to_i }]}]
end

def nested_iter
  A.each_with_object({}) {|e,r| e.each {|k,v| (r[k] ||= []) << v.to_i } }
end

cases = %w{to_a_flat to_a_flat_construct group_by_each group_by_each_construct nested_iter}

N = 250_000

puts RUBY_DESCRIPTION
Benchmark.bmbm(25) do |x|
  cases.each do |the_case|
    x.report(the_case) { N.times { send the_case } }
  end
end