Assign First Element of Nested Array as Property of Parent Object

Question

Assuming the following Array:

[
{id: 1234, name: "@Acme", sources:["Twitter"]},
{id: 5678, name: "@Enron", sources:["Facebook"]},
]

I want to promote sources[0] to a property value, either under sources itself or as a new key using lodash.

I've done the following:

myList = _.map(monitorList, _.partialRight(_.pick, ['id', 'name', 'sources']));
mySources = _.map(monitorList, 'sources');

I imagine I can iterate through each respective array now and map my index from mySources to the sources key in myList, however it seems like there should be a functional way using lodash to promote a nested array item to a property value.

Ideal final data structure:

[
{id: 1234, name: "@Acme", sources:"Twitter"},
{id: 5678, name: "@Enron", sources:"Facebook"},
]

Could you also show the intended output structure you want to achieve? — tony
– tony, Commented Jul 11, 2017 at 15:45

trincot · Accepted Answer · 2017-07-11 17:53:48Z

2

With a functional ES6 approach:

const monitorList = [
    {id: 1234, name: "@Acme", sources:["Twitter"]},
    {id: 5678, name: "@Enron", sources:["Facebook"]},
];

var result = monitorList.map(o => Object.assign({}, o, { sources: o.sources[0] }));

console.log(result);

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

answered Jul 11, 2017 at 17:53

trincot

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Comments

Alberto Trindade Tavares · Accepted Answer · 2017-07-11 17:56:14Z

1

You can follow a simple path and use forEach to replace sources property:

var items = [{id: 1234, name: "@Acme", sources:["Twitter"]},
             {id: 5678, name: "@Enron", sources:["Facebook"]}];

items.forEach((item) => item.sources = item.sources[0]);

console.log(items);

Another solution, using map, which is more functional (as it does not change items variable):

var items = [{id: 1234, name: "@Acme", sources:["Twitter"]},
             {id: 5678, name: "@Enron", sources:["Facebook"]}];

var newItems = items.map((item) => Object.assign({}, item, { sources: item.sources[0] }));

console.log(newItems);

edited Jul 11, 2017 at 17:56

answered Jul 11, 2017 at 17:39

Alberto Trindade Tavares

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7 Comments

terpinmd Over a year ago

Note that doing it this way mutates the original array. That could be ok but its not very functional.

Alberto Trindade Tavares Over a year ago

@terpinmd. That's true. Edite my answer to include a more functional solution. Thanks!

Tyler Mills Over a year ago

I wanted an answer in lodash, but it's pretty similar and I didn't care about mutation of the original array in this case, so your solution put me on the right path: _.forEach(monitorList, monitor => monitor.sources = monitor.sources[0]);

Alberto Trindade Tavares Over a year ago

Yeah, _.forEach ends up being equivalent to Array.prototype.forEach

trincot Over a year ago

@TylerMills, I'm a bit confused how to reconcile "there should be a functional way" with "I didn't care about mutation".

|

terpinmd · Accepted Answer · 2017-07-11 17:54:47Z

1

You could use map:

var array = [{id: 1234, name: "@Acme", sources:["Twitter"]},
              {id: 5678, name: "@Enron", sources:["Facebook"]}];


var items = array.map(item => {
  item.source = item.sources[0]; 
  return item;
});

You could change item.source to item.sources as well if you wanted to overwrite.

Another way using some losdash methods:

var items = array.map(item => {
  return _.assign({}, item, {sources: _.first(item.sources)});
});

edited Jul 11, 2017 at 17:54

answered Jul 11, 2017 at 17:41

terpinmd

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