Measures performance of loops iterating with pairs, ipairs and indexing

perf-iterators.lua

#!/usr/bin/env luajit

--[[

Environment: Lenovo ThinkPad X200 / 16GB RAM / iCore7 2620M (2.70GHz, 4MB Cache)

|  pairs   |  ipairs  | indexing |
| 1.000000 | 5.244480 | 9.388388 |
| 0.190677 | 1.000000 | 1.790146 |
| 0.106515 | 0.558614 | 1.000000 |

]]--

local function array(n)
   local result = {}
   for i=1, n do
      table.insert(result, tostring(i))
   end
   return result
end

local function execute_times(f, times)
   local a = array(100)
   local begin = os.clock()
   for i=1,times do
      f(a)
   end
   local finish = os.clock()
   return finish - begin
end

local times = {}
local ITERATIONS = 1000000

-- Pairs
local elapse_time = execute_times(function(a) 
   for j,v in pairs(a) do
      x=v
   end
end, ITERATIONS)
times["pairs"] = elapse_time

-- iPairs
local elapse_time = execute_times(function(a) 
   for _,v in ipairs(a) do
      x=v
   end
end, ITERATIONS)
times["ipairs"] = elapse_time

-- Indexing
local elapse_time = execute_times(function(a) 
   for j=1,#a do
      x=v
   end
end, ITERATIONS)
times["indexing"] = elapse_time

local results = {
   { times["pairs"]/times["pairs"], times["pairs"]/times["ipairs"], times["pairs"]/times["indexing"] },
   { times["ipairs"]/times["pairs"], times["ipairs"]/times["ipairs"], times["ipairs"]/times["indexing"] },
   { times["indexing"]/times["pairs"], times["indexing"]/times["ipairs"], times["indexing"]/times["indexing"] },
}
print("|  pairs   |  ipairs  | indexing |")
for _, row in ipairs(results) do
   io.write(string.format("| %.6f ", row[1]))
   io.write(string.format("| %.6f |", row[2]))
   io.write(string.format(" %.6f |", row[3]))
   io.write("\n")
end

Line 54 should be x=a[j] then the results will change to

|  pairs   |  ipairs  | indexing |
| 1.000000 | 3.133077 | 2.923984 |
| 0.319175 | 1.000000 | 0.933263 |
| 0.341999 | 1.071509 | 1.000000 |