Question

我试图从用作字典的对象中随机选择一个随机属性，以进行快速索引。

考虑以下代码：

//Create test dictionary
var dict = {};
for(var i = 0; i < 10000; i++) {
  var num = Math.random() * 1000000 << 0;
  dict[num] = { Id: num };
}

//Fuzz
const NUM_RUNS = 1000;
var start = new Date();
for(var i = 0; i < NUM_RUNS; i++)
  getRandom(dict);
var end = new Date();

var runTime = (end.getTime() - start.getTime()) / 1000;
var timePerCall = (runTime / NUM_RUNS) * Math.pow(10,9);
console.log('Total Calls: ' + NUM_RUNS);
console.log('Total Runtime: ' + runTime + ' seconds');
console.log('Time Per Call: ' + timePerCall + ' nanoseconds');



function getRandom(dict) {
  var keys = Object.keys(dict);
  var index = keys[Math.random() * keys.length << 0];
  return dict[index];
}

如您所见，Object.keys()的使用非常昂贵，尤其是随着词典的增长。

我正在寻找实现字典中元素随机选择的最佳方法。当然，在字典中包含10000+个元素是一个极端的情况，但是我仍然希望能够处理它。

Answer 1

如果无法缓存Object.keys数组，则可以使用Proxy维护自己的副本：

function generateKeyTracker (keysPropertyName) {
  const set = new Set();
  function defineProperty (target, property, descriptor) {
    target[property] = descriptor.value;

    if (set.has(property)) return true;

    set.add(property);
    target[keysPropertyName].push(property);
    return true;
  }
  function deleteProperty (target, property) {
    delete target[property];
    
    if (!set.delete(property)) return true;

    target[keysPropertyName] = target[keysPropertyName].filter(key => key !== property);
    return true;
  }
  return {defineProperty, deleteProperty};
}

//Create test dictionary
var dict = new Proxy(
  Object.defineProperty({}, '__keys', {
    configurable: true,
    enumerable: false,
    writable: true,
    value: []
  }),
  generateKeyTracker('__keys')
);

for(var i = 0; i < 1e4; i++) {
  var num = Math.random() * 1e6 << 0;
  dict[num] = { Id: num };
}

//Fuzz
const NUM_RUNS = 1e6;
var start = performance.now();
for(var i = 0; i < NUM_RUNS; i++)
  getRandom(dict);
var end = performance.now();

var runTime = end - start;
var timePerCall = (runTime / NUM_RUNS);
console.log(`Total Calls: ${NUM_RUNS}`);
console.log(`Total Runtime: ${runTime} ms`);
console.log(`Time Per Call: ${timePerCall * 1e6} ns`);

function getRandom(dict) {
  var index = Math.random() * dict.__keys.length << 0;
  return dict[dict.__keys[index]];
}

这使用property creation和deletion上的陷阱来跟踪dict的属性键，这些属性键存储在non-enumerable属性dict.__keys中。 / p>

JavaScript：对象键的快速随机索引

1 个答案: