Grouping Nested Objects with Dynamic Keys (Using Lodash)

Question

I'm querying Firebase to get some data to throw into Chart.js. Here's how I've laid out my data:

{
  "20160428": {
    "follow": 13,
    "host": 6,
    "raid": 1,
    "substreak": 1,
    "tip": 1
  },
  "20160429": {
    "follow": 15,
    "host": 21,
    "raid": 2,
    "substreak": 4
  },
  "20160430": {
    "follow": 4
  },
  "20160501": {
    "follow": 11,
    "host": 15,
    "subscription": 4,
    "substreak": 5
  },
  "20160502": {
    "follow": 2,
    "host": 6,
    "subscription": 1,
    "substreak": 4
  },
  "20160503": {
    "follow": 2
  }
}

As you can see, each object is keyed off by a timestamp and events don't always appear in every object (but there are a finite number of events). Here's how I'd like the data to look so I can feed it into Chart.js:

labels: ["20160428", "20160429", "20160430", ...]

{
  "follow": [13, 15, 4, 11, 2, 2],
  "host": [6, 21, 0, 15, 6, 0],
  "raid": [1, 2, 0, 0, 0, 0],
  "subscription": [0, 0, 0, 4, 1, 0]
  "substreak": [1, 4, 0, 5, 4, 0]
  "tip": [1, 0, 0, 0, 0, 0]
}

I've played with Lodash's groupBy and similar functions, but I'm not sure if I'm on the right track. I wouldn't mind doing this x times either per event, but at this point I can't change the schema.

Answer 1

If you have a defined set of keys that you want to group then you have to:

1. Use map() to pluck values with compact() to get non-null values from the object collection from the defined set of keys.

2. Build the result using zipObject() from the defined keys and values obtained from the first step.

---

var keys = ["follow", "host", "raid", "substreak", "tip", "subscription"];
var values = _.map(keys, key => _(data).map(key).compact().value());
var result = _.zipObject(keys, values);

var data = {
  "20160428": { "follow": 13, "host": 6, "raid": 1, "substreak": 1, "tip": 1 },
  "20160429": { "follow": 15, "host": 21, "raid": 2, "substreak": 4 },
  "20160430": { "follow": 4 },
  "20160501": { "follow": 11, "host": 15, "subscription": 4, "substreak": 5 },
  "20160502": { "follow": 2, "host": 6, "subscription": 1, "substreak": 4 },
  "20160503": { "follow": 2 }
};

var keys = ["follow", "host", "raid", "substreak", "tip", "subscription"];
var values = _.map(keys, key => _(data).map(key).compact().value());
var result = _.zipObject(keys, values);

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.11.2/lodash.js"></script>

If you want to group them from all the keys present in the object collection then you can:

1. Get all the unique keys by:

   • map() each data object inside the object collection
   • flatten() the resulting array
   • Use uniq() to get all unique keys from the flattened array.

2. Use the methodology in the first example to get the values and build the object.

---

var keys = _(data).map(_.keys).flatten().uniq().value();
var values = _.map(keys, key => _(data).map(key).compact().value());
var result = _.zipObject(keys, values);

var data = {
  "20160428": { "follow": 13, "host": 6, "raid": 1, "substreak": 1, "tip": 1 },
  "20160429": { "follow": 15, "host": 21, "raid": 2, "substreak": 4 },
  "20160430": { "follow": 4 },
  "20160501": { "follow": 11, "host": 15, "subscription": 4, "substreak": 5 },
  "20160502": { "follow": 2, "host": 6, "subscription": 1, "substreak": 4 },
  "20160503": { "follow": 2 }
};

var keys = _(data).map(_.keys).flatten().uniq().value();
var values = _.map(keys, key => _(data).map(key).compact().value());
var result = _.zipObject(keys, values);

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.11.2/lodash.js"></script>