SRANDMEMBER lacks randomness

prng.js

/**
 * Module dependencies.
 */

var crypto = require('crypto')
  , rrange = 4294967296;

/**
 * Return an integer, pseudo-random number in the range [0, 2^32).
 */

var nextInt = function() {
  return crypto.randomBytes(4).readUInt32BE(0);
};

/**
 * Return a floating-point, pseudo-random number in the range [0, 1).
 */

var rand = function() {
  return nextInt() / rrange;
};

/**
 * Return an integer, pseudo-random number in the range [0, max).
 */

var randInt = function(max) {
  return Math.floor(rand() * max);
};

exports.randInt = randInt;

results_card_100

SRANDMEMBER results
===================

least_extracted: {elem: 14, count: 35} most_extracted: {elem: 99, count: 65} mean_value: 50 std_dev: 6.989992846920518
least_extracted: {elem: 38, count: 34} most_extracted: {elem: 27, count: 72} mean_value: 50 std_dev: 7.135825109964509
least_extracted: {elem: 58, count: 32} most_extracted: {elem: 0, count: 69} mean_value: 50 std_dev: 7.173562573784381
least_extracted: {elem: 0, count: 37} most_extracted: {elem: 68, count: 66} mean_value: 50 std_dev: 6.619667665374147
least_extracted: {elem: 88, count: 36} most_extracted: {elem: 31, count: 71} mean_value: 50 std_dev: 6.592419889539804
least_extracted: {elem: 98, count: 35} most_extracted: {elem: 19, count: 71} mean_value: 50 std_dev: 7.2
least_extracted: {elem: 78, count: 28} most_extracted: {elem: 5, count: 65} mean_value: 50 std_dev: 7.67984374841051
least_extracted: {elem: 39, count: 34} most_extracted: {elem: 8, count: 67} mean_value: 50 std_dev: 6.685805860178712
least_extracted: {elem: 62, count: 32} most_extracted: {elem: 0, count: 66} mean_value: 50 std_dev: 6.777905281132217
least_extracted: {elem: 57, count: 34} most_extracted: {elem: 31, count: 65} mean_value: 50 std_dev: 6.606057825965498
least_extracted: {elem: 87, count: 35} most_extracted: {elem: 53, count: 68} mean_value: 50 std_dev: 6.871681017043792
least_extracted: {elem: 89, count: 35} most_extracted: {elem: 40, count: 68} mean_value: 50 std_dev: 6.37808748764079
least_extracted: {elem: 31, count: 38} most_extracted: {elem: 46, count: 64} mean_value: 50 std_dev: 6.348228099241551
least_extracted: {elem: 5, count: 32} most_extracted: {elem: 8, count: 66} mean_value: 50 std_dev: 6.592419889539804
least_extracted: {elem: 9, count: 35} most_extracted: {elem: 0, count: 67} mean_value: 50 std_dev: 7.052659073002182
least_extracted: {elem: 76, count: 34} most_extracted: {elem: 80, count: 69} mean_value: 50 std_dev: 6.925315877272314
least_extracted: {elem: 20, count: 37} most_extracted: {elem: 54, count: 64} mean_value: 50 std_dev: 5.854912467321779
least_extracted: {elem: 77, count: 33} most_extracted: {elem: 7, count: 68} mean_value: 50 std_dev: 6.606057825965498
least_extracted: {elem: 64, count: 32} most_extracted: {elem: 61, count: 66} mean_value: 50 std_dev: 6.442049363362563
least_extracted: {elem: 22, count: 33} most_extracted: {elem: 15, count: 71} mean_value: 50 std_dev: 7.500666637039671
least_extracted: {elem: 29, count: 29} most_extracted: {elem: 15, count: 71} mean_value: 50 std_dev: 6.820557161991974
least_extracted: {elem: 29, count: 36} most_extracted: {elem: 42, count: 72} mean_value: 50 std_dev: 7.12460525222275
least_extracted: {elem: 14, count: 35} most_extracted: {elem: 22, count: 74} mean_value: 50 std_dev: 7.994998436522674
least_extracted: {elem: 54, count: 31} most_extracted: {elem: 83, count: 75} mean_value: 50 std_dev: 7.96994353806851
least_extracted: {elem: 17, count: 37} most_extracted: {elem: 91, count: 70} mean_value: 50 std_dev: 7.1693793315739685
least_extracted: {elem: 72, count: 32} most_extracted: {elem: 32, count: 72} mean_value: 50 std_dev: 6.841052550594828
least_extracted: {elem: 55, count: 33} most_extracted: {elem: 97, count: 68} mean_value: 50 std_dev: 6.143289021363068
least_extracted: {elem: 7, count: 33} most_extracted: {elem: 40, count: 68} mean_value: 50 std_dev: 7.183313998427188
least_extracted: {elem: 11, count: 34} most_extracted: {elem: 55, count: 66} mean_value: 50 std_dev: 7.222188034107115
least_extracted: {elem: 58, count: 32} most_extracted: {elem: 74, count: 71} mean_value: 50 std_dev: 7.677239087067694

PRNG + ZRANGE results
=====================

least_extracted: {elem: 38, count: 34} most_extracted: {elem: 19, count: 75} mean_value: 50 std_dev: 7.725283166331186
least_extracted: {elem: 66, count: 32} most_extracted: {elem: 88, count: 72} mean_value: 50 std_dev: 7.386474125047755
least_extracted: {elem: 85, count: 30} most_extracted: {elem: 13, count: 67} mean_value: 50 std_dev: 6.387487769068525
least_extracted: {elem: 70, count: 35} most_extracted: {elem: 55, count: 62} mean_value: 50 std_dev: 6.041522986797286
least_extracted: {elem: 21, count: 33} most_extracted: {elem: 11, count: 65} mean_value: 50 std_dev: 6.81175454637056
least_extracted: {elem: 66, count: 34} most_extracted: {elem: 20, count: 69} mean_value: 50 std_dev: 7.3006848993775915
least_extracted: {elem: 41, count: 36} most_extracted: {elem: 23, count: 69} mean_value: 50 std_dev: 7.035623639735144
least_extracted: {elem: 60, count: 29} most_extracted: {elem: 8, count: 72} mean_value: 50 std_dev: 6.789698078707183
least_extracted: {elem: 36, count: 35} most_extracted: {elem: 80, count: 64} mean_value: 50 std_dev: 6.6257075093909785
least_extracted: {elem: 65, count: 34} most_extracted: {elem: 2, count: 70} mean_value: 50 std_dev: 7.15122367151245
least_extracted: {elem: 8, count: 33} most_extracted: {elem: 54, count: 66} mean_value: 50 std_dev: 6.395310782127793
least_extracted: {elem: 64, count: 29} most_extracted: {elem: 54, count: 68} mean_value: 50 std_dev: 6.502307282803543
least_extracted: {elem: 70, count: 33} most_extracted: {elem: 61, count: 68} mean_value: 50 std_dev: 6.860029154456998
least_extracted: {elem: 3, count: 29} most_extracted: {elem: 73, count: 70} mean_value: 50 std_dev: 6.955573304911681
least_extracted: {elem: 36, count: 35} most_extracted: {elem: 43, count: 76} mean_value: 50 std_dev: 7.603946343840151
least_extracted: {elem: 29, count: 35} most_extracted: {elem: 75, count: 69} mean_value: 50 std_dev: 7.12460525222275
least_extracted: {elem: 34, count: 33} most_extracted: {elem: 58, count: 68} mean_value: 50 std_dev: 8.027452896155792
least_extracted: {elem: 71, count: 35} most_extracted: {elem: 22, count: 62} mean_value: 50 std_dev: 6.281719509815764
least_extracted: {elem: 8, count: 30} most_extracted: {elem: 29, count: 66} mean_value: 50 std_dev: 7.6589816555466435
least_extracted: {elem: 29, count: 34} most_extracted: {elem: 16, count: 67} mean_value: 50 std_dev: 5.96322060635023
least_extracted: {elem: 25, count: 36} most_extracted: {elem: 26, count: 74} mean_value: 50 std_dev: 7.645913941446111
least_extracted: {elem: 42, count: 34} most_extracted: {elem: 56, count: 71} mean_value: 50 std_dev: 7.487322618933954
least_extracted: {elem: 82, count: 34} most_extracted: {elem: 10, count: 67} mean_value: 50 std_dev: 7.240165743959181
least_extracted: {elem: 92, count: 32} most_extracted: {elem: 71, count: 70} mean_value: 50 std_dev: 7.567033764957046
least_extracted: {elem: 0, count: 30} most_extracted: {elem: 49, count: 67} mean_value: 50 std_dev: 6.739436178197699
least_extracted: {elem: 7, count: 38} most_extracted: {elem: 97, count: 80} mean_value: 50 std_dev: 6.865857557508749
least_extracted: {elem: 51, count: 38} most_extracted: {elem: 8, count: 70} mean_value: 50 std_dev: 6.473020933072903
least_extracted: {elem: 41, count: 27} most_extracted: {elem: 34, count: 68} mean_value: 50 std_dev: 7.397296803562772
least_extracted: {elem: 50, count: 36} most_extracted: {elem: 52, count: 69} mean_value: 50 std_dev: 6.590902821313632
least_extracted: {elem: 12, count: 33} most_extracted: {elem: 24, count: 73} mean_value: 50 std_dev: 7.385120175054703

results_card_1000

SRANDMEMBER results
===================

least_extracted: {elem: 286, count: 10} most_extracted: {elem: 706, count: 103} mean_value: 50 std_dev: 23.725808732264532
least_extracted: {elem: 669, count: 7} most_extracted: {elem: 108, count: 108} mean_value: 50 std_dev: 23.422126291180312
least_extracted: {elem: 295, count: 5} most_extracted: {elem: 645, count: 110} mean_value: 50 std_dev: 24.2488350235635
least_extracted: {elem: 983, count: 7} most_extracted: {elem: 648, count: 104} mean_value: 50 std_dev: 23.780832617887878
least_extracted: {elem: 286, count: 7} most_extracted: {elem: 689, count: 110} mean_value: 50 std_dev: 23.937167752263427
least_extracted: {elem: 286, count: 7} most_extracted: {elem: 116, count: 105} mean_value: 50 std_dev: 23.733225655186445
least_extracted: {elem: 605, count: 7} most_extracted: {elem: 130, count: 103} mean_value: 50 std_dev: 23.860553220744904
least_extracted: {elem: 901, count: 8} most_extracted: {elem: 247, count: 104} mean_value: 50 std_dev: 23.62773793658631
least_extracted: {elem: 535, count: 8} most_extracted: {elem: 657, count: 112} mean_value: 50 std_dev: 23.700928251863893
least_extracted: {elem: 798, count: 7} most_extracted: {elem: 422, count: 105} mean_value: 50 std_dev: 23.603813251252433
least_extracted: {elem: 983, count: 7} most_extracted: {elem: 42, count: 109} mean_value: 50 std_dev: 23.718811100053056
least_extracted: {elem: 295, count: 8} most_extracted: {elem: 308, count: 101} mean_value: 50 std_dev: 23.525305524052182
least_extracted: {elem: 605, count: 4} most_extracted: {elem: 589, count: 111} mean_value: 50 std_dev: 23.548630533430178
least_extracted: {elem: 759, count: 4} most_extracted: {elem: 405, count: 105} mean_value: 50 std_dev: 24.09207338524437
least_extracted: {elem: 798, count: 4} most_extracted: {elem: 342, count: 106} mean_value: 50 std_dev: 24.119286888297506
least_extracted: {elem: 259, count: 5} most_extracted: {elem: 825, count: 104} mean_value: 50 std_dev: 24.01478711127792
least_extracted: {elem: 592, count: 5} most_extracted: {elem: 67, count: 104} mean_value: 50 std_dev: 23.789241265748682
least_extracted: {elem: 798, count: 7} most_extracted: {elem: 634, count: 104} mean_value: 50 std_dev: 23.723111094458076
least_extracted: {elem: 605, count: 9} most_extracted: {elem: 655, count: 105} mean_value: 50 std_dev: 23.751336804483238
least_extracted: {elem: 286, count: 6} most_extracted: {elem: 446, count: 107} mean_value: 50 std_dev: 23.792435772740884
least_extracted: {elem: 259, count: 3} most_extracted: {elem: 711, count: 103} mean_value: 50 std_dev: 23.670065483644105
least_extracted: {elem: 759, count: 6} most_extracted: {elem: 845, count: 107} mean_value: 50 std_dev: 23.82217454389922
least_extracted: {elem: 901, count: 4} most_extracted: {elem: 345, count: 103} mean_value: 50 std_dev: 23.711937921646133
least_extracted: {elem: 259, count: 7} most_extracted: {elem: 924, count: 104} mean_value: 50 std_dev: 23.810753872987725
least_extracted: {elem: 605, count: 8} most_extracted: {elem: 238, count: 105} mean_value: 50 std_dev: 23.951033380628903
least_extracted: {elem: 295, count: 7} most_extracted: {elem: 97, count: 103} mean_value: 50 std_dev: 23.80294099475945
least_extracted: {elem: 759, count: 4} most_extracted: {elem: 54, count: 108} mean_value: 50 std_dev: 23.780201849437695
least_extracted: {elem: 798, count: 6} most_extracted: {elem: 872, count: 104} mean_value: 50 std_dev: 23.61855203013089
least_extracted: {elem: 916, count: 5} most_extracted: {elem: 449, count: 101} mean_value: 50 std_dev: 23.82565843791101
least_extracted: {elem: 266, count: 7} most_extracted: {elem: 28, count: 105} mean_value: 50 std_dev: 23.510253082431927

PRNG + ZRANGE results
=====================

least_extracted: {elem: 371, count: 31} most_extracted: {elem: 111, count: 75} mean_value: 50 std_dev: 7.1442284397967
least_extracted: {elem: 639, count: 32} most_extracted: {elem: 745, count: 73} mean_value: 50 std_dev: 7.13792686989717
least_extracted: {elem: 119, count: 31} most_extracted: {elem: 644, count: 78} mean_value: 50 std_dev: 7.252172088415994
least_extracted: {elem: 890, count: 25} most_extracted: {elem: 769, count: 74} mean_value: 50 std_dev: 6.8625068305976935
least_extracted: {elem: 43, count: 30} most_extracted: {elem: 553, count: 78} mean_value: 50 std_dev: 7.0861837402088295
least_extracted: {elem: 398, count: 26} most_extracted: {elem: 350, count: 73} mean_value: 50 std_dev: 7.022962337931196
least_extracted: {elem: 432, count: 29} most_extracted: {elem: 393, count: 77} mean_value: 50 std_dev: 7.471679864662297
least_extracted: {elem: 319, count: 27} most_extracted: {elem: 830, count: 75} mean_value: 50 std_dev: 7.141568455178456
least_extracted: {elem: 634, count: 24} most_extracted: {elem: 758, count: 76} mean_value: 50 std_dev: 6.822316322188527
least_extracted: {elem: 513, count: 29} most_extracted: {elem: 137, count: 73} mean_value: 50 std_dev: 6.925027075759344
least_extracted: {elem: 240, count: 29} most_extracted: {elem: 119, count: 71} mean_value: 50 std_dev: 6.948812848249692
least_extracted: {elem: 754, count: 28} most_extracted: {elem: 180, count: 75} mean_value: 50 std_dev: 7.033775657497188
least_extracted: {elem: 491, count: 28} most_extracted: {elem: 211, count: 72} mean_value: 50 std_dev: 7.031073886683314
least_extracted: {elem: 993, count: 31} most_extracted: {elem: 384, count: 74} mean_value: 50 std_dev: 7.208883408684039
least_extracted: {elem: 544, count: 25} most_extracted: {elem: 356, count: 86} mean_value: 50 std_dev: 7.2280011068067775
least_extracted: {elem: 87, count: 31} most_extracted: {elem: 120, count: 72} mean_value: 50 std_dev: 7.11083680026479
least_extracted: {elem: 334, count: 29} most_extracted: {elem: 403, count: 76} mean_value: 50 std_dev: 6.993711461019821
least_extracted: {elem: 693, count: 26} most_extracted: {elem: 489, count: 74} mean_value: 50 std_dev: 7.240165743959181
least_extracted: {elem: 414, count: 29} most_extracted: {elem: 216, count: 76} mean_value: 50 std_dev: 7.253826576366436
least_extracted: {elem: 167, count: 28} most_extracted: {elem: 140, count: 78} mean_value: 50 std_dev: 7.237679186037469
least_extracted: {elem: 4, count: 29} most_extracted: {elem: 643, count: 74} mean_value: 50 std_dev: 7.01612428624237
least_extracted: {elem: 867, count: 27} most_extracted: {elem: 156, count: 72} mean_value: 50 std_dev: 7.338255923582933
least_extracted: {elem: 568, count: 28} most_extracted: {elem: 524, count: 80} mean_value: 50 std_dev: 7.120954992134131
least_extracted: {elem: 96, count: 30} most_extracted: {elem: 536, count: 76} mean_value: 50 std_dev: 6.928347566339322
least_extracted: {elem: 262, count: 29} most_extracted: {elem: 383, count: 75} mean_value: 50 std_dev: 7.188741197177709
least_extracted: {elem: 26, count: 32} most_extracted: {elem: 663, count: 72} mean_value: 50 std_dev: 6.835641886465382
least_extracted: {elem: 239, count: 29} most_extracted: {elem: 194, count: 74} mean_value: 50 std_dev: 6.782477423478828
least_extracted: {elem: 645, count: 28} most_extracted: {elem: 378, count: 73} mean_value: 50 std_dev: 7.131199057662042
least_extracted: {elem: 991, count: 31} most_extracted: {elem: 327, count: 81} mean_value: 50 std_dev: 7.124184163818338
least_extracted: {elem: 67, count: 31} most_extracted: {elem: 338, count: 73} mean_value: 50 std_dev: 6.81850423480106

stat.js

/**
 * Return the element extracted the smallest number of times.
 */

var leastExtracted = function(values) {
  var item = {
    elem: Number.MAX_VALUE,
    count: Number.MAX_VALUE
  };
  values.forEach(function(val, i) {
    if (val < item.count) {
      item.elem = i;
      item.count = val;
    }
  });
  return item;
};

/**
 * Return the average of the values.
 */

var mean = function(values) {
  var sum = 0;
  values.forEach(function(val) {
    sum += val; 
  });
  return sum / values.length;
};

/**
 * Return the element extracted the biggest number of times.
 */

var mostEtracted = function(values) {
  var item = {
    elem: Number.MIN_VALUE,
    count: Number.MIN_VALUE
  };
  values.forEach(function(val, i) {
    if (val > item.count) {
      item.elem = i;
      item.count = val;
    }
  });
  return item;
};

/**
 * Return the standard deviation of the values.
 */

var std_dev = function(values) {
  var average = mean(values)
    , sum = 0
    , variance;
  values.forEach(function(val) {
    sum += Math.pow(val - average, 2);
  });
  variance = sum / values.length;
  return Math.sqrt(variance);
};

exports.leastExtracted = leastExtracted;
exports.mean = mean;
exports.mostEtracted = mostEtracted;
exports.std_dev = std_dev;

test.js

/**
 * Module dependencies.
 */

var async = require('async')
  , rc = require('redis').createClient()
  , sample = []
  , number_of_samples = 30
  , mode = 'SRANDMEMBER'
  , randInt = require('./prng').randInt
  , sample_size = 1000
  , draws_per_sample = sample_size * 50
  , stat = require('./stat');

/**
 * Add an element in the set.
 */

var addElement = function(element) {
  var args = ['set', element]
    , command = 'SADD';
  if (mode === 'PRNG + ZRANGE') {
    args.push(element);
    command = 'ZADD';
  }
  return function(callback) {
    rc.send_command(command, args, callback);
  };
};

/**
 * Get sample data and print the result.
 */

var getSample = function() {
  if (!number_of_samples) {
    if (mode === 'SRANDMEMBER') {
      mode = 'PRNG + ZRANGE';
      number_of_samples = 30;
      console.log('\nPRNG + ZRANGE results\n=====================\n');
      return start();
    }
    rc.quit();
    console.log();
    return;
  }
  number_of_samples--;
  resetSample();
  var tasks = [];
  for (var i = 0; i < draws_per_sample; i++) {
    tasks.push(randElement);
  }
  async.parallel(tasks, function(err, elements) {
    if (err) {
      throw err;
    }
    var least = stat.leastExtracted(sample)
      , most = stat.mostEtracted(sample)
      , meanval = stat.mean(sample)
      , stddev = stat.std_dev(sample);

    console.log('least_extracted: {elem: '+least.elem+', count: '+least.count+'}'
      +' most_extracted: {elem: '+most.elem+', count: '+most.count+'}'
      +' mean_value: '+meanval+' std_dev: '+stddev);

    getSample();
  });
};

/**
 * Return a random element from the set.
 */

var randElement = function(callback) {
  var args = ['set']
    , command = 'SRANDMEMBER';
  if (mode === 'PRNG + ZRANGE') {
    var start = randInt(sample_size)
      , stop = start;
    args = args.concat([start, stop]);
    command = 'ZRANGE';
  }
  rc.send_command(command, args, function(err, element) {
    if (err) {
      return callback(err);
    }
    if (typeof element === 'object') {
      element = element[0];
    }
    element = parseInt(element, 10);
    sample[element]++;
    callback(null, element);
  });
};

/**
 * Reset the sample.
 */

var resetSample = function() {
  for (var i = 0; i < sample_size; i++) {
    sample[i] = 0;
  }
};

/**
 * Start the test.
 */

var start = function() {
  rc.send_command('DEL', ['set'], function(err, result) {
    if (err) {
      throw err;
    }
    var tasks = [];
    for (var i = 0; i < sample_size; i++) {
      tasks.push(addElement(i));
    }
    async.parallel(tasks, function(err, results) {
      if (err) {
        throw err;
      }
      getSample();
    });
  });
};

console.log('\nSRANDMEMBER results\n===================\n');
start();