Avoiding Nesting Maps When "pivoting" Multidimensional Array

I have data in the format [ { 'timeline_map': { '2017-05-06': 770, '2017-05-07': 760, '2017-05-08': 1250 ... } }, { 'timeline_map': {

Solution 1:

You could use a closure over a hash table and assign the values accordingly to the date keys.

var data = [{ timeline_map: { "2017-05-06": 770, "2017-05-07": 760, "2017-05-08": 1250 } }, { timeline_map: { "2017-05-06": 590, "2017-05-07": 210, "2017-05-08": 300 } }, { timeline_map: { "2017-05-06": 890, "2017-05-07": 2200, "2017-05-08": 1032 } }],
    grouped = data.reduce(function (hash) {
        returnfunction (r, o) {
            Object.keys(o.timeline_map).forEach(function (k) {
                if (!hash[k]) {
                    hash[k] = [k];
                    r.push(hash[k]);
                }
                hash[k].push(o.timeline_map[k]);
            });
            return r;
        };
    }(Object.create(null)), []);

console.log(grouped);

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Solution 2:

Merge the objects using _.mergeWith(), and then _.map() the resulting object to an array of arrays:

const arr = [{
    "timeline_map": {
      "2017-05-06": 770,
      "2017-05-07": 760,
      "2017-05-08": 1250
    }
  },
  {
    "timeline_map": {
      "2017-05-06": 590,
      "2017-05-07": 210,
      "2017-05-08": 300
    }
  },
  {
    "timeline_map": {
      "2017-05-06": 890,
      "2017-05-07": 2200,
      "2017-05-08": 1032
    }
  }
];

const result = _.map(_.mergeWith({}, ...arr, (o1, o2) => {
  if(Array.isArray(o1)) {
    o1.push(o2)
    return o1;
  }
  
  if(_.isNumber(o2)) {
    return [o2];
  }
}).timeline_map, (v, k) => [k, ...v]);

console.log(result);

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