How to extract a sample of objects from array of nested objects

Question

i'm developing in Javascript and i created folders array that contain objects:

folders = [folder1, folder2, folder3...]

Every object have some properties, one of this is docs that is an array of objects:

docs = [doc1, doc2, doc3...]

...and every object is like this:

doc1.title = 'foo'
doc1.desc = 'bar'
doc1.attr = {new: _.random(0, 1) > 0.5, read: _.random(0, 1) > 0.5}
...

I would like to create a function that extract only docs that have attr = {new: true, read: false}. I tried some underscore method such as _.each, _.sample, _.find and _.findWhere, but i can't figure out how to get from the main array a sample that contains docs with that attr properties.

Any idea?

Could you give us more code? Like what did you try with lodash .find()? Wouldn't a regular loop do the work? — Cohars
– Cohars, Commented Mar 10, 2016 at 14:13
remark: do not use new without quotes as a key of object. use "new" instead. — Dmitriy
– Dmitriy, Commented Mar 10, 2016 at 14:20
I added a working JSFiddle to my answer, tell me if it fits your needs. — Cohars
– Cohars, Commented Mar 10, 2016 at 14:54

Gruff Bunny · Accepted Answer · 2016-03-12 10:46:12Z

1

Using underscore first flatten the folders and then use where to get what you want:

var result = _.where( _.flatten(folders), {new: true, read: false});

Edited to work with the new structure:

var result = _.chain(folders)
    .pluck('docs')
    .flatten()
    .where({isNew: true, read: false})
    .value();

var folders = [
	{
		docs: [				
			{
				title: 'one',
				isNew: true,
				read: false
			},				{
				title: 'two',
				isNew: true,
				read: true
			}
		]
	},
	{
		docs: 
		[
			{
				title: 'three',
				isNew: false,
				read: false
			},				{
				title: 'four',
				isNew: true,
				read: false
			}
		]
	}
];

var result = _.chain(folders)
	.pluck('docs')
	.flatten()
	.where({isNew: true, read: false})
	.value();

document.getElementById('result').textContent = JSON.stringify(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.8.2/underscore.js"></script>

<p>
  <pre id="result"></pre>
</p>

edited Mar 12, 2016 at 10:46

answered Mar 10, 2016 at 14:28

Gruff Bunny

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5 Comments

smartmouse Over a year ago

I didn't know _.flatten, anyway i was wrong and i edited my answer. Can you make your way working with the new structure?

Cohars Over a year ago

Underscore or lodash are not really required here, but this should work indeed.

Gruff Bunny Over a year ago

Apart from when you don't want to reinvent the wheel and when you want to support older browsers.

smartmouse Over a year ago

It doens't work, anyway it doesn't matter because i found a solution. Thank you anyway.

Gruff Bunny Over a year ago

Added a code snippet and also changed the code to reflect that the doc property new is now called isNew.

Tolokoban · Accepted Answer · 2016-03-10 14:17:54Z

0

Have you tried something like this?

var result = [];
folders.forEach(function(docs) {
    result.concat( docs.filter(function(doc) {
        return doc.attr.new && !doc.attr.read;
    });
});

answered Mar 10, 2016 at 14:17

Tolokoban

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Comments

Tomer · Accepted Answer · 2016-03-10 14:18:50Z

0

underscore methods like .find work on arrays which are one level deep:

 var temp = [];
_.each(folders , function(docsArray){
    var result = _.where(docsArray ,  {new: true, read: false});
    if(result){
        temp.concat(result);
    }
});

answered Mar 10, 2016 at 14:18

Tomer

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Comments

ismnoiet · Accepted Answer · 2016-03-10 14:19:14Z

0

You can achieve what you want without using underscore or lodash,just Take advantage of the built-in Array.map and Array.filter methods, here is an example :

var myResult = folders.map(function(folder){

      return myCustomDocs = folder.filter(function(doc){
            return (doc.attr.new  && !doc.attr.read);
      });
});

console.log(myResult);

answered Mar 10, 2016 at 14:19

ismnoiet

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Comments

Cohars · Accepted Answer · 2016-03-11 10:21:26Z

0

What about a regular filter?

Working Demo

(Simply open your browser console and run the fiddle.)

doc1.filter(o => o.attr.new && !o.attr.read)

And you can also simply map() your folders array.

const _folders = folders
  .map(doc => doc.filter(o => o.attr.new && !o.attr.read))

You would get on new folders array containing arrays with only new && !read documents. Which you could flatten if needed:

const flatFolders = [].concat.apply([], _folders)

edited Mar 11, 2016 at 10:21

answered Mar 10, 2016 at 14:17

Cohars

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Comments

smartmouse · Accepted Answer · 2016-03-11 13:34:34Z

0

I found a working solution. Here is my code:

var result = [];
folders.forEach(function(item) {
    result = result.concat(_.filter(item.docs, function(doc) {
        return doc.isNew === true && doc.read === false;
    }));
});

answered Mar 11, 2016 at 13:34

smartmouse

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Comments

zangw · Accepted Answer · 2016-03-11 13:40:18Z

0

If you have Node.js 5+ or use Babel, you can just do:

folders.reduce((res, arr) => res.concat(arr), [])      // flatten folders
       .filter(doc => doc.attr.new && !doc.attr.read); // remove all that don't return true

edited Mar 11, 2016 at 13:40

zangw

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answered Mar 10, 2016 at 14:39

gregers

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