demo_iteration.rb

require 'benchmark'
require 'active_support'

@col_map = (1..30).map{|i| ["a#{i}", "b#{i}"]}
@row = Hash[(1..30).map{|i| ["b#{i}", i]}]

def orig(row)
  Hash[@col_map.map{|cn, an| [cn, row[an]]}]
end

def naive(row)
  hash = {}

  index = 0
  while index < @col_map.length do
    cn,an = @col_map[index]
    hash[cn] = row[an]
    index += 1
  end

  hash
end

def each_with_object(row)
  @col_map.each_with_object({}) do |(cn, an), hash|
    hash[cn]= row[an]
  end
end


Benchmark.bmbm do |x|
  x.report("original") do
    10000.times{ orig(@row) }
  end

  x.report("naive") do
    10000.times{ naive(@row) }
  end

  x.report("each_with_object") do
    10000.times{ each_with_object(@row)}
  end
end

Rehearsal ----------------------------------------------------
original           0.080000   0.010000   0.090000 (  0.091959)
naive              0.080000   0.010000   0.090000 (  0.082822)
each_with_object   0.090000   0.000000   0.090000 (  0.093846)
------------------------------------------- total: 0.270000sec

                       user     system      total        real
original           0.090000   0.000000   0.090000 (  0.087676)
naive              0.080000   0.000000   0.080000 (  0.077203)
each_with_object   0.090000   0.000000   0.090000 (  0.087767)

Neat. It's always nice to see some stats. I also played with checking heap usage in addition to time, and got results like this:

original: 1516
naive: 758
each_with_object: 783