Merge javascript objects in object with same value

Question

I have been trying to combine objects with same value. The object that I have is like this:

{
  'Mon': [{'apple': 'A', 'color': 'green'}, {'apple':'B', 'color':'yellow'}],
  'Tue': [{'apple': 'A', 'color': 'green'}, {'apple':'B', 'color':'yellow'}],
  'Wed': [],
  'Thu': [],
  'Fri': [{'banana': 'A', 'color': 'yellow'}],
  'Sat': [{'banana': 'A', 'color': 'yellow'}],
  'Sun': [{'banana': 'A', 'color': 'yellow'}]
}

I have been trying to find a way to combine these so that the result would be like this:

{
  ['Mon', 'Tue']: [{'apple': 'A', 'color': 'green'}, {'apple':'B','color':'yellow'}],
  ['Wed', 'Thu']: [],
  ['Fri','Sat','Sun']: [{'banana': 'A', 'color': 'yellow'}]
}

Is there some way to do this with lodash ? or pure js ?

That result is invalid data format.

Nenad Vracar
– Nenad Vracar

2017-02-07 14:58:37 +00:00
Commented Feb 7, 2017 at 14:58 — Nenad Vracar
– Nenad Vracar, Commented Feb 7, 2017 at 14:58

rpadovani · Accepted Answer · 2017-02-07 15:31:07Z

In Javascript the keys of an object have to be strings.

However, you can use arrays, they will be casted to string:

var a = {};

a[['Mon', 'Tue']] = 1;

console.log(a[['Mon', 'Tue']])
console.log(a)

But, of course, they keys of the final object would be string. Anyway, should be trivial to create a function to convert them back to array, if you need them.

About processing the data, I'd go like this:

var original = {
  'Mon': [{'apple': 'A', 'color': 'green'}, {'apple':'B', 'color':'yellow'}],
  'Tue': [{'apple': 'A', 'color': 'green'}, {'apple':'B', 'color':'yellow'}],
  'Wed': [],
  'Thu': [],
  'Fri': [{'banana': 'A', 'color': 'yellow'}],
  'Sat': [{'banana': 'A', 'color': 'yellow'}],
  'Sun': [{'banana': 'A', 'color': 'yellow'}]
};

var emptyKey = [];

function createId(o) {
  var values = [];
  
  for (let x in o) {
    if (o.hasOwnProperty(x)) {
      values.push(o[x])
    }
  }
  return Object.keys(o).sort().toString() + values.sort().toString();
}

var uniqueValues = [];

for (let d in original) {
  for (let b in original[d]) {
    let idx = createId(original[d][b]);
    if (uniqueValues.indexOf(idx) === -1) uniqueValues.push(idx);
  }

  if (Object.keys(original[d]).length === 0) emptyKey.push(d);
}

var result = {};

for (let u in uniqueValues) {
  let k = [];
  let o = null;
  
  for (let d in original) {
    for (let b in original[d]) {
      let idx = createId(original[d][b]);
      if (uniqueValues[u] === idx) {
        k.push(d);
        o = original[d][b];
      }
    }
  }
  
  if (k.length > 0) {
     result[k] = result[k] || [];
     result[k].push(o);
  }
}

if (emptyKey.length > 0) result[emptyKey] = [];

console.log(result)

However, some caveats of the solution:

As said, keys are string, not arrays, but anyway you can access them using arrays (because they have the toString() method).
The order in which the keys are printed is theoretical not guaranteed, and this is why I use the sort() method - also if all the major browsers will print them in the order they are inserted

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