Grouping objects by multiple columns with Lodash or Underscore

Question

I have following object records :

 {  
   "notes":[  
      {  
         "id":1,
         "description":"hey",
         "userId":2,
         "replyToId":null,
         "postId":2,
         "parentId":null
      },
      {  
         "id":5,
         "description":"hey test",
         "userId":3,
         "replyToId":null,
         "postId":2,
         "parentId":null
      },
      {  
         "id":2,
         "description":"how are you",
         "userId":null,
         "replyToId":2,
         "postId":2,
         "parentId":null,
         "user":null
      }
   ]
}

I want to output it as:

2 
  object with id 1
  object with id 2 (because replyToId value is same as userId
3
  object with id 5

So basically I want to consider UserId and replyToId value under the same group.

I have build my own mixin under lodash, wrapping groupBy method as:

mixin({
    splitGroupBy: function(list, groupByIter){
        if (_.isArray(groupByIter)) {
            function groupBy(obj) {
                return _.forEach(groupByIter, function (key){
                    if ( !!obj[key] ) return obj[key]
                });

            }
        } else {
            var groupBy = groupByIter;
        }

        debugger;

        var groups = _.groupBy(list, groupBy);

        return groups;
    }
});

Call looks like this:

_.splitGroupBy(data.notes,['userId', 'replyToId']);

The output is coming without group. Even when I have tried with _.map instead _.forEach the split is not happening correctly.

Answer 1

A solution using underscore:

    var props = ['userId', 'replyToId'];

    var notNull = _.negate(_.isNull);

    var groups = _.groupBy(record.notes, function(note){
        return _.find(_.pick(note, props), notNull);
    });

Answer 2

This can probably done much prettier, but it should work:

lodash.mixin({
  splitGroupBy: function(list, groupByIter) {
    var _ = this, groupBy;
    if (lodash.isArray(groupByIter)) {
      groupBy = function(obj) {
        return _(obj) .pick(groupByIter)
                      .values()
                      .without(null, undefined)
                      .first();
      };
    } else {
      groupBy = groupByIter;
    }
    var groups = _.groupBy(list, groupBy);
    return groups;
  }
});

Answer 3

You can use stringify object as key.

_.groupBy(notes, ({ userId, replyToId }) => JSON.stringify({ userId, replyToId }));

output:

{
  "{\"userId\":2,\"replyToId\":null}": [
    {
      "id": 1,
      "description": "hey",
      "userId": 2,
      "replyToId": null,
      "postId": 2,
      "parentId": null
    }
  ],
  "{\"userId\":3,\"replyToId\":null}": [
    {
      "id": 5,
      "description": "hey test",
      "userId": 3,
      "replyToId": null,
      "postId": 2,
      "parentId": null
    }
  ],
  "{\"userId\":null,\"replyToId\":2}": [
    {
      "id": 2,
      "description": "how are you",
      "userId": null,
      "replyToId": 2,
      "postId": 2,
      "parentId": null,
      "user": null
    }
  ]
}

Answer 4

You could map your list of attributes to their respective values and pick the first non falsy value as your group key:

_.mixin({
    splitGroupBy: function(list, groupByIter){
        if (!_.isArray(groupByIter))
            return _.groupBy(list, groupByIter);

        return _.groupBy(list, function(o) {
            var values = _.map(groupByIter, function(k) {
                return o[k];
            });
            return _.find(values);
        });
    }
});

 var data = { "notes":[ { "id":1, "userId":2, "replyToId":null }, { "id":5, "userId":3, "replyToId":null }, { "id":2, "userId":null, "replyToId":2 } ] }; _.mixin({ splitGroupBy: function(list, groupByIter){ if (!_.isArray(groupByIter)) return _.groupBy(list, groupByIter); return _.groupBy(list, function(o) { var values = _.map(groupByIter, function(k) { return o[k]; }); return _.find(values); }); } }); snippet.log(JSON.stringify(_.splitGroupBy(data.notes,['userId', 'replyToId'])));

 <script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.3/underscore-min.js"></script> <!-- Provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 --> <script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

Answer 5

Assuming userId and replyToId are mutually exclusive (ie you either have a userId or a replyToId , but never both) as they are in the sample data, then specifying a custom grouping function works:

_.groupBy(data.notes, function(note) {
    return note.userId || note.replyToId;
});