Javascript Merge/filter array

Question

Given the following json object:

var posts = {
    [0] : {
        "name": "X",
        "categories" : [1, 5, 6]
    },
    [1] : {
        "name": "Y",
        "categories" : [1, 5, 7]
    }
}

How can I get a single array containing every "categories" property value, without repetitions?

In this case, I would like to retrieve something like

var objCategories = [1, 5, 6, 7];

Please learn the difference between [objects](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer) and [arrays](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array). Your definition of `posts` is very strange. — str, Oct 10 '17 at 09:09
I'm voting to close this question as off-topic because the question shows input and output format but not any sign of effort. This makes question a requirement and not a problem statement — Rajesh, Oct 10 '17 at 09:11
You can refer to following links: **[Group based on property](https://stackoverflow.com/questions/31688459/group-array-items-using-object)** and **[Remove duplicates from array](https://stackoverflow.com/questions/9229645/remove-duplicates-from-javascript-array)** and play around(*merge*) to get the final solution. — Rajesh, Oct 10 '17 at 09:13

score 1 · Answer 1 · answered Oct 10 '17 at 09:18

In a ES6 enabled environment, you can use a Set and reduce

let objCategories = [...new Set(Object.values(posts).reduce((a,b) => a.concat(b.categories), []))];

let posts = {
  [0]: {
    "name": "X",
    "categories": [1, 5, 6]
  },
  [1]: {
    "name": "Y",
    "categories": [1, 5, 7]
  }
};
let cats = [...new Set(Object.values(posts).reduce((a, b) => a.concat(b.categories), []))];
console.log(cats);

gurvinder372 · Answer 2 · 2017-10-10T09:16:47.073

0

something like

var objCategories = {}; //create a map for all unique keys
Object.keys(posts).forEach( function(index){
  var post = posts[ index ]; //get access to the object
  post.categories.forEach( function(cat){
    objCategories[ cat ] = cat;  
  });
});
objCategories = Object.keys( objCategories ); //get only the arrays of categories and assign them back to objCategories for desired result

edited Oct 10 '17 at 09:16

answered Oct 10 '17 at 09:10

gurvinder372

66,980
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That'll result in `TypeError: posts.forEach is not a function` because it is not an array, it's an object. – Sven Oct 10 '17 at 09:13
@Svenskunganka try again now – gurvinder372 Oct 10 '17 at 09:14
1

@Rayon yes, my bad – gurvinder372 Oct 10 '17 at 09:15
Please add explanation. *something like* will not help anyone – Rajesh Oct 10 '17 at 09:15

notrota · Answer 3 · 2017-10-10T09:20:07.210

do

var posts = {
    [0] : {
        "name": "X",
        "categories" : [1, 5, 6]
    },
    [1] : {
        "name": "Y",
        "categories" : [1, 5, 7]
    }
}

// logic
var merged = []; // get all of the categories
for (let name in posts) { // loop through name
  var post = posts[name]; // get post
  merged = merged.concat(post.categories); // add categories
}
var unique = merged.filter(function(item, pos, self) { // filter duplicates
    return self.indexOf(item) == pos;
});
console.log(unique);

exp:

this gathers all the categories

for (let name in posts) { // loop through name
  var post = posts[name]; // get post
  merged = merged.concat(post.categories); // add categories
}

the result will be

[1, 5, 6, 1, 5, 7]

then this filters out the duplicates:

var unique = merged.filter(function(item, pos, self) { // filter duplicates
    return self.indexOf(item) == pos;
});

the result is"

[1, 5, 6, 7]

what? it solves the question - he asked to find all the unique categories — notrota, Oct 10 '17 at 09:17
My point was about your explanation. *do* does not explain what and why are you doing what you are doing. You are answering for readers and not just OP. — Rajesh, Oct 10 '17 at 09:18

score 0 · Answer 4 · answered Oct 10 '17 at 09:16

You have to loop through the object:

var posts = {
    [0] : {
        "name": "X",
        "categories" : [1, 5, 6]
    },
    [1] : {
        "name": "Y",
        "categories" : [1, 5, 7]
    }
}
var objCategories = [];

Object.values(posts).forEach(post => { 
    post.categories.forEach(c => {
        if (objCategories.indexOf(c) === -1) {
            objCategories.push(c);
        }
    })
});

console.log(objCategories);

score 0 · Answer 5 · answered Oct 10 '17 at 09:19

Use reduce and forEach:

var posts = {
    [0] : {
        "name": "X",
        "categories" : [1, 5, 6]
    },
    [1] : {
        "name": "Y",
        "categories" : [1, 5, 7]
    }
};

var result = Object.keys(posts).reduce(function (categories, key) {
  posts[key].categories.forEach(function (category) {
    if (categories.indexOf(category) === -1) {
      categories.push(category);
    }
  });
  return categories;
}, []);

console.log(result);

Javascript Merge/filter array

5 Answers5