LUAJIT Comparison of pairs, ipairs and indexing

paris-ipairs-index-bench.lua

#!/usr/bin/env luajit

--[[
Adapted from https://gist.github.com/dpino/647b9d2e12aa8ff859b4

Environment: Lenovo ThinkPad T520 / 16GB RAM / i7-3740QM CPU @ 2.70GHz

|  pairs   |  ipairs  | indexing |
| 1.000000 | 4.283464 | 4.058733 |
| 0.233456 | 1.000000 | 0.947535 |
| 0.246382 | 1.055370 | 1.000000 |
]]--

local ITERATIONS = 1000000

local x

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 = {}

-- Pairs
local elapse_time1 = execute_times(function(a)
    for j,v in pairs(a) do
        x=v
    end
end, ITERATIONS)
times["pairs"] = elapse_time1

-- iPairs
local elapse_time2 = execute_times(function(a)
    for _,v in ipairs(a) do
        x=v
    end
end, ITERATIONS)
times["ipairs"] = elapse_time2

-- Indexing
local elapse_time3 = execute_times(function(a)
    local len = #a
    for j=1,len do
        x=a[j]
    end
end, ITERATIONS)
times["indexing"] = elapse_time3

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