Lua script for viewing the shape of the native Lua random generator, seeded by the time.

random-histogrammer.lua

local lower = 1
local upper = 20
local numSamples = arg[1] or 1000
local numTrials = 10
local hist  = {}
local getSeed  = coroutine.create(
    function()
        local start
        while true do
            start = os.time()
            coroutine.yield(os.time())
            -- Allow some time to pass so the seed value can change enough
            while os.difftime(os.time(), start) < 1 do end
        end
    end
)

local seed, subject = 0, 0
local sample = {}

function printHistogram(data, width, prefix)
    local min, max = nil, nil
    local adjusted

    table.sort(data)

    -- Calculate data bounds
    for k, v in pairs(data) do
        if min == nil or v < min then
            min = v
        end
        if max == nil or v > max then
            max = v
        end
    end

    for k, v in pairs(data) do
        adjusted = (v / max) * width
        print(string.format("%s%2d|%s (%d)", prefix, k, string.rep('=', adjusted), v))
    end
end

for trial = 1, numTrials do
    print(string.format("Trial #%d:", trial))
    err, seed = coroutine.resume(getSeed)
    print(string.format("\tSeed=%s", tostring(seed)))

    math.randomseed(seed)

    -- Initialize the sample to zero-count for all numbers between lower and upper bounds
    sample = {}
    for i = lower, upper do sample[i] = 0 end

    -- Generate the sample
    for subjectNum = 1, numSamples do
        subject = math.random(lower, upper)
        sample[subject] = sample[subject] + 1
    end

    -- Print indented histogram
    printHistogram(sample, 20, '\t')

    -- Save the sample
    table.insert(hist, sample)
end