lodash pick object fields from array

Question

I have array of objects:

var results= [
    {         
      "_type": "MyType",
      "_id": "57623535a44b8f1417740a13",         
      "_source": {
        "info": {
          "year": 2010,
          "number": "string",             
        },
        "type": "stolen",           
        "date": "2016-06-16T00:00:00",
        "createdBy": "57469f3c71c8bf2479d225a6"            
      }
    }
  ];

I need to select specific fields from array. In result, I want to get the following:

[
    {
        "_id": "57623535a44b8f1417740a13",
        "info": {
            "year": 2010,
            "number": "string"
        },
        "type": "stolen",            
        "date": "2016-06-16T00:00:00",
        "createdBy": "57469f3c71c8bf2479d225a6"
    }
]

As you can see, I want to select _id field and content of _source object. How can I do this with lodash?

I've found .map function, but it doesn't take array of keys: var res = _.map(results, "_source");

Let Me Tink About It · Accepted Answer · 2018-11-04 20:04:58Z

63

You could do:

var mapped = _.map(results, _.partialRight(_.pick, ['_id', 'info', 'type', 'date', 'createdBy']));

A little explanation:

_.map(): Expects a function which takes each item from the collection so that you can map it to something else.
_.partialRight(): Takes a function which will be called later on with the its arguments appended to the end
_.pick(): Gets the path specified from the object.

edited Nov 4, 2018 at 20:04

Let Me Tink About It

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answered Jul 12, 2017 at 20:43

radyz

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2 Comments

Nebulosar Over a year ago

I find partial hard to read, so I want to suggest just using an arrow function instead: var mapped = _.map(results, obj => _.pick(obj, ['_id', 'info', 'type', 'date', 'createdBy']));

Claytronicon Over a year ago

This won't account for the OPs request to pick items out of "_source", but not _source itself. Given the nested input object, this would return [{"_id":"57623535a44b8f1417740a13"}]

Hardik Raval · Accepted Answer · 2020-05-04 12:28:40Z

6

I had the same requirement, and the below solution worked best for me.

let users = [
{
  "_id": "5ead7783ed74d152f86de7b0",
  "first_name": "User First name 1",
  "last_name": "User Last name 1",
  "email": "[email protected]",
  "phone": 9587788888
},
{
  "_id": "5ead7b780d4bc43fd0ef92e7",
  "first_name": "User FIRST name 1",
  "last_name": "User LAST name 1",
  "email": "[email protected]",
  "phone": 9587788888
}
 ];

users = users.map(user => _.pick(user,['_id','first_name']))

console.log(users)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

answered May 4, 2020 at 12:28

Hardik Raval

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Comments

Nina Scholz · Accepted Answer · 2016-06-17 09:39:02Z

5

In plain Javascript you could iterate with Array#map and assemble a new object for each object without mutilation the original object.

var results = [{ "_type": "MyType", "_id": "57623535a44b8f1417740a13", "_source": { "info": { "year": 2010, "number": "string", }, "type": "stolen", "date": "2016-06-16T00:00:00", "createdBy": "57469f3c71c8bf2479d225a6" } }],
    res = results.map(function (a) {
        var o = { _id: a._id };
        ["info", "type", "date", "createdBy"].forEach(function (k) {
            o[k] = a._source[k];
        });
        return o;
    });

console.log(res);

answered Jun 17, 2016 at 9:39

Nina Scholz

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1 Comment

user348173 Over a year ago

Thanks for the answer, I know how to do it with plain JS, my plain code looks almost the same as your, but I use lodash a lot, for reduce code size, for readability and so on and look the way if I can do this with lodash

Mikhail Shabrikov · Accepted Answer · 2017-10-03 15:00:02Z

1

var results = [{
  _type: "MyType",
  _id: "57623535a44b8f1417740a13",
  _source: {
    info: {
      year: 2010,
      number: "string",
    },
    type: "stolen",
    date: "2016-06-16T00:00:00",
    createdBy: "57469f3c71c8bf2479d225a6"
  }
}];

var rootProperty = ['_id']
var innerProperty = '_source'

var myArray = _.map(results, result => _(result)
  .pick(rootProperty)
  .assign(_.result(result, innerProperty))
  .value()
)

console.log(myArray)

.as-console-wrapper { max-height: 100% !important; top: 0; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.min.js"></script>

edited Oct 3, 2017 at 15:00

answered Jun 17, 2016 at 10:03

Mikhail Shabrikov

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Comments

ryeballar · Accepted Answer · 2016-06-18 13:41:51Z

You can map() the result and have each item assign() the _id key-value in an object toegether with the _source object.

results = _.map(results, item => _.assign(
  { _id: item._id }, 
  item._source
));

var results = [{
  "_type": "MyType",
  "_id": "57623535a44b8f1417740a13",
  "_source": {
    "info": {
      "year": 2010,
      "number": "string",
    },
    "type": "stolen",
    "date": "2016-06-16T00:00:00",
    "createdBy": "57469f3c71c8bf2479d225a6"
  }
}];

results = _.map(results, item => _.assign(
  { _id: item._id }, 
  item._source
));

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

<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>

You may also choose to write this in plain JS:

result = results.map(item => Object.assign(
  { _id: item._id }, item._source
));

var results = [{
  "_type": "MyType",
  "_id": "57623535a44b8f1417740a13",
  "_source": {
    "info": {
      "year": 2010,
      "number": "string",
    },
    "type": "stolen",
    "date": "2016-06-16T00:00:00",
    "createdBy": "57469f3c71c8bf2479d225a6"
  }
}];

result = results.map(item => Object.assign(
  { _id: item._id }, item._source
));

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

Orwellophile · Accepted Answer · 2023-01-30 13:26:20Z

To correctly fulfill the OP's question and for even more complex requirements, the application of a schema and a small lodash mixin is invaluable.

The JavaScript is a little ugly, but it looks swell in CoffeeScript (yes, that was a thing once). The compiled JavaScript is hidden beneath.

_.mixin mapGet: (obj, schema) ->
  result = for row in input
    row_result = {}
    for key, value of schema
      row_result[key] = _.get(row, value)
    row_result

_.mixin({ mapGet: function(obj, schema) {
    var key, result, row, row_result, value;
    return result = (function() {
        var i, len, results;
        results = [];
        for (i = 0, len = input.length; i < len; i++) {
            row = input[i];
            row_result = {};
            for (key in schema) {
                value = schema[key];
                row_result[key] = _.get(row, value);
            }
            results.push(row_result);
        }
        return results;
    })();
}});

/* The remainer is just the proof/usage example */

var expected, input, schema;

input = [{
"_type": "MyType",
"_id": "57623535a44b8f1417740a13",
"_source": {
  "info": {
    "year": 2010,
    "number": "string"
  },
  "type": "stolen",
  "date": "2016-06-16T00:00:00",
  "createdBy": "57469f3c71c8bf2479d225a6"
}}];

expected = [{
"_id": "57623535a44b8f1417740a13",
"info": {
  "year": 2010,
  "number": "string"
},
"type": "stolen",
"date": "2016-06-16T00:00:00",
"createdBy": "57469f3c71c8bf2479d225a6"
}];

schema = {
  "_id": "_id",
  "info": "_source.info",
  "type": "_source.type",
  "date": "_source.date",
  "createdBy": "_source.createdBy"
};

console.log('expected result: ' + JSON.stringify(expected, 0, 4));
console.log('actual result:   ' + JSON.stringify(_.mapGet(input, schema), 0, 4));

<script src="https://cdn.jsdelivr.net/lodash/4/lodash.min.js"></script>

Usage:

schema = {
  "_id"      : "_id",
  "info"     : "_source.info",
  "type"     : "_source.type",
  "date"     : "_source.date",
  "createdBy": "_source.createdBy",
}

_.mapGet(input, schema)

Resultant output:

[{
    "_id": "57623535a44b8f1417740a13",
    "info": {
        "year": 2010,
        "number": "string"
    },
    "type": "stolen",
    "date": "2016-06-16T00:00:00",
    "createdBy": "57469f3c71c8bf2479d225a6"
}]

Note: Complex schema can be more easily described if the source JSON is first converted to a flat, dotted, representation via:

jq [leaf_paths as $path | {"key":$path | join("."), "value":getpath($path) }] |from_entries'

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