How to get array of objects with unique values?

Question

How to sum object array with the same key value?

I have this array:

let arrData = [{ category: "Main Expenses", amount: 420 },
    { category: "Food", amount: 50 },
    { category: "Main Expenses", amount: 4530},
    { category: "Food", amount: 4520 },
    { category: "Main Expenses", amount: 4530 },
    { category: "Food", amount: 450 },
    { category: "Self Care", amount: 7540 },
    { category: "Child Care", amount: 4570 }]

And I need to get array with unique categories, like this:

[Main Expenses: 9480,
Food: 5020,
Self Care: 7540,
Child Care: 4570]

Your "like this" array is not valid JavaScript. So, before people start trying to answer your question, please edit it and make clear what's your expected outcome. — Gerardo Furtado
– Gerardo Furtado, Commented Jun 7, 2019 at 5:44

brk · Accepted Answer · 2019-06-07 06:00:22Z

3

The expected output is in array is not possible since array will not support key & value pair. You may opt for object.

You can use reduce and check if the object contains the key by category name. If so then add the amount otherwise create key by the category name and set its value to the amount

let arrData = [{
    category: "Main Expenses",
    amount: 420
  },
  {
    category: "Food",
    amount: 50
  },
  {
    category: "Main Expenses",
    amount: 4530
  },
  {
    category: "Food",
    amount: 4520
  },
  {
    category: "Main Expenses",
    amount: 4530
  },
  {
    category: "Food",
    amount: 450
  },
  {
    category: "Self Care",
    amount: 7540
  },
  {
    category: "Child Care",
    amount: 4570
  }
]

let newData = arrData.reduce((acc, item) => {
  acc[item.category] = acc[item.category] ?
    acc[item.category] + item.amount :
    item.amount;
  return acc;
}, {});

console.log(newData)

edited Jun 7, 2019 at 6:00

answered Jun 7, 2019 at 5:45

brk

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5 Comments

Shubham Dixit Over a year ago

@sandrooco pls make sure that you don't change the answer context while editing

sandrooco Over a year ago

@Shubh What does changing the answer context mean in that case?

Shubham Dixit Over a year ago

When i upvoted the answer was working properly ,after you edited it started giving Nan,I dint quite saw what yoou edited @sandrooco

Shubham Dixit Over a year ago

@brk,I guess the question asks for array and your result returns an object ,probably user wants two dim array ?

sandrooco Over a year ago

1. It was some other dude's edit that gave NaN. 2. You can see all edits by clicking on "edited x minutes ago". 3. There's nothing about context, it's just not working properly. 4. I suppose @Kate needs an object to know about the categories' keys.

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