在javascript中按值排序

Question

I have an object with many-to-one mapping:

{
  'a' : 'one',
  'b' : 'two',
  'c' : 'one',
  'd' : 'two'
}

Now I want to make the following object from this:

{
  'one' : ['a' , 'c'],
  'two' : ['b' , 'd']
}

What is the most efficient way to do this in javascript (we can also use underscore libraries if it helps) Note: The above objects are just a shorter version of the actual problem.

Answer 1

var data = {
  'a' : 'one',
  'b' : 'two',
  'c' : 'one',
  'd' : 'two'
}

var result = {};

for(var key in data) {
    var val = data[key];
    if(!result[val]) result[val] = [];

    result[val].push(key);
}

console.log(result);

Answer 2

You can do this with Object.keys() and reduce

 var data = {'a': 'one','b': 'two','c': 'one','d': 'two'} var result = Object.keys(data).reduce((res, e) => { res[data[e]] = (res[data[e]] || []).concat(e); return res; }, {}); console.log(result)

You could also use forEach and add to created object

 var data = {'a': 'one','b': 'two','c': 'one','d': 'two'}, r = {} Object.keys(data).forEach(e => {r[data[e]] = (r[data[e]] || []).concat(e)}); console.log(r)

Answer 3

Well, here's my approach. Not as advanced as Nenad's though.

var obj = {
  'a' : 'one',
  'b' : 'two',
  'c' : 'one',
  'd' : 'two'
};

var result = {};

for (var i in obj) {
  if (obj[i] in result) {
    result[obj[i]].push(i);
  } else {
    result[obj[i]] = [i];
  }
}

console.log(result);

Answer 4

a single liner

 var map = { 'a' : 'one', 'b' : 'two', 'c' : 'one', 'd' : 'two' }, reduced = Object.keys(map).reduce((p,c) => {!!p[map[c]] ? p[map[c]].push(c) : p[map[c]] = [c]; return p},{}) document.write("<pre>" + JSON.stringify(reduced) + "</pre>");