Javascript - 添加两个 HashMap

Question

我有两个 HashMap 如下

m1={};
m1['a']={};
m1['b']={};
m1['a']['x']=5;
m1['b']['x']=6;
m1['a']['y']=4;
m1['b']['y']=6;

m2={};
m2['a']={};
m2['b']={};
m2['a']['x']=8;
m2['b']['x']=7;
m2['a']['y']=6;
m2['b']['y']=4;

output expected
m3['a']['x']->13;
m3['a']['y']->10;
m3['b']['x']->13;
m3['b']['y']->10;

一个简单的解决方案是遍历每个 map 并向新 map 添加值，但是有没有更有效的方法？

Answer 1

您可以使用Object.entries 将对象转换为数组。使用 reduce

汇总数组

let m1 = {};
m1['a'] = {};
m1['b'] = {};
m1['a']['x'] = 5;
m1['b']['x'] = 6;
m1['a']['y'] = 4;
m1['b']['y'] = 6;


let m2 = {};
m2['a'] = {};
m2['b'] = {};
m2['a']['x'] = 8;
m2['b']['x'] = 7;
m2['a']['y'] = 6;
m2['b']['y'] = 4;
m2['a']['z'] = "name";

let m3 = Object.entries(m1).reduce((c, [i, v]) => {
  let addOnly = ['x', 'y'];
  c[i] = c[i] || {};

  //Loop thru m1
  Object.entries(v).reduce((x, [k, o]) => Object.assign(x, {[k]: o}), c[i]);

  //Loop thru m2 
  Object.entries(m2[i]).reduce((x, [k, o]) => {

    if (addOnly.includes(k)) {
      x[k] = x[k] || 0;
      x[k] += o;
    } else {
      x[k] = x[k] || o;
    }

    return x;
  }, c[i]);

  return c;
}, {})

console.log(m3);