Remove duplicates from an array of objects in JavaScript But merge one field before removing the duplicates

Question

I have the following variable:

var allProducts = [
    {"code": 1,"name": "productA", "category": ["fruits"],...},
    {"code": 1,"name": "productA", "category": ["vegetables"],...},
    {"code": 2,"name": "productB", "category": ["meat"],...},
    ...
]

So the only difference between the two repeated array of objects is the category; where in this example code: 1 is once mentioned with category: ["fruits"] and another time with category: ["vegetables"]. Now I want to remove the duplicate but before doing so; I would like to save all the categories of productA into one category: ["fruits", "vegetables"] so the final variable would look like this:

var allProductsCleaned = [ 
    {"code": 1,"name": "productA", "category": ["fruits", "vegetables"],...},
    {"code": 2,"name": "productB", "category": ["meat"]...},
    ...
]

I think you put wrong object, key type in the variable. It should be like this? var allProducts = [ {"code": 1,"name": "productA", "category": ["fruits"],...},... — Kevin Lee
– Kevin Lee, Commented Apr 28, 2020 at 6:57
Does this answer your question? merging duplicates in javascript array — Gregoire
– Gregoire, Commented Apr 28, 2020 at 10:50

Alex L · Accepted Answer · 2020-04-30 18:04:06Z

2

Here's an example:

Create an object with reduce:
- save each object into the aggregated Object to test if "code" already added
- if already present then merge the arrays
transform the object back to an array with Object.values()

const allProducts = [
    {"code": 1,"name": "productA", "category": ["fruits"]},
    {"code": 1,"name": "productA", "category": ["vegetables"]},
    {"code": 2,"name": "productB", "category": ["meat"]},
    {"code": 2,"name": "productB", "category": ["fish"]},
    {"code": 2,"name": "productB", "category": ["fish"]}
]

const output = Object.values(allProducts.reduce((aggObj, item) => {  
  if (aggObj[item.code]){
    //item already exists so merge the category arrays:
    const newArr = [...new Set([...aggObj[item.code].category, ...item.category])]
    aggObj[item.code].category = newArr;
  }else{
    //doesn't already exist:
    aggObj[item.code] = item;
  }  
  return aggObj
}, {}));

console.log(output);

edited Apr 30, 2020 at 18:04

answered Apr 30, 2020 at 13:26

Alex L

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3 Comments

user12669401 Over a year ago

Perfect! This is exactly what I was looking for. Thank you Alex! Quick question if the product with code 1 here; have the same category for both as ["fruits"]; with your above code it will merge it and output the category as ` ["fruits", "fruits" ]. Right? How can I prevent that when if the category array` contains the word fruit to not merge them?

Alex L Over a year ago

Great, See my updated answer - we can use the ES6 new Set([iterable]) to ensure unique entries (there are other ways to do it, like using arr.inlcudes(item)). If my answer solved your problem please consider to mark as the accepted answer and up-vote :)

user12669401 Over a year ago

You are awesome! upvoted and accepted as answer! thank you

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