Merge array of complex objects by using Lodash

Question

I'm new to Lodash and trying to solve this problem but could find a good way to do it.

I have an array of objects return back from the database. The data is structured as below:

var data = [{
    index: 1,
    Aoo: "a1",
    Boo: 'b2',
}, {
    index: 1,
    Aoo: "a2",
    Boo: 'b2',
}, {
    index: 2,
    Aoo: "a3",
    Boo: 'b3',
}];

I want to first group the objects by index, then group the attribute "Aoo" and "Boo" and put it in an array attribute called param.

var result = [{
        index: 1,
        param: [{
            Aoo: 'A1',
            Boo: 'B1'
        },{
            Aoo: 'A2',
            Boo: 'B2',
        }]
    }, {
        index: 2,
        param: [{
            Aoo: 'A3',
            Boo: 'B3'
        }]
   }
]

I can do it manually but I want to make the most use of Lodash's functionality. Right now I only know I can achieve the first step of grouping by using _.groupBy('index') and I am stuck at what to do next.

VLAZ · Accepted Answer · 2016-09-21T07:22:59.203

You are almost there. Here is how this can be done using lodash

var data = [{
    index: 1,
    Aoo: "a1",
    Boo: 'b2',
}, {
    index: 1,
    Aoo: "a2",
    Boo: 'b2',
}, {
    index: 2,
    Aoo: "a3",
    Boo: 'b3',
}];

var result = _.chain(data)
  .groupBy('index')
  .map((value, key) => {
    return {
      index: Number(key), //the index was transformed into a string, this will make it a number again.
      param: _.map(value, o => _.omit(o, 'index'))//do not include the index key from the previous objects
    }
  })
  .value();

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.16.1/lodash.min.js"></script>

The second part is, admittedly, slightly trickier than the grouping, but not by much. Since indexing gives you this structure:

{
  "1": [
    {
      "index": 1,
      "Aoo": "a1",
      "Boo": "b2"
    },
    {
      "index": 1,
      "Aoo": "a2",
      "Boo": "b2"
    }
  ],
  "2": [
    {
      "index": 2,
      "Aoo": "a3",
      "Boo": "b3"
    }
  ]
}

All you really want to do is go over it, make each key be the index property and then you are left with an array of the inital objects. Each needs to be transformed by removing the index key and that will be assigned to the param value. This is done in one go using .map. Unfortunately, it's not as pretty as it could look but I think that's the best you can do with the base version of Lodash.

If you want to select a specific subset of the keys, instead of "all but index", then you can use _.pick instead of _.omit to do it. Here is how this would look:

var data = [{
    index: 1,
    Aoo: "a1",
    Boo: 'b2',
    Coo: "c1"
}, {
    index: 1,
    Aoo: "a2",
    Boo: 'b2',
    Coo: "c2"
}, {
    index: 2,
    Aoo: "a3",
    Boo: 'b3',
    Coo: "c3"
}];

var result = _.chain(data)
  .groupBy('index')
  .map((value, key) => {
    return {
      index: Number(key), //the index was transformed into a string, this will make it a number again.
      param: _.map(value, o => _.pick(o, ['Aoo', 'Boo']))//do not include the index key from the previous objects
    }
  })
  .value();

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.16.1/lodash.min.js"></script>

So we get the same result even though there is an extra key in the data.

Was a few seconds behind posting literally a character for character answer :) — Matt Way, Sep 20 '16 at 23:25
thank you for the fast response! I do have a follow up question. What if i have more attributes that doesn't want to get include? Do i need to map it one by one? for example: `{Aoo: "a", Boo: "b", Coo: "c", Doo: "d"}` and I only want to combine `Boo` and `Coo`? thanks! — CocoHot, Sep 21 '16 at 03:49
If you only want to select specific properties use `_.pick()` instead of `_.omit()`, since it does the opposite. — VLAZ, Sep 21 '16 at 05:46

Merge array of complex objects by using Lodash

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