How to get repeated objects in json array in javascript

Question

I have a JSON array like this :

var data = [
      {title: "HH02"},
      {title: "HH03"},
      {title: "HH04"},
      {title: "HH02"},
      {title: "HH07"},
      {title: "HH08"},
      {title: "HH08"},
      {title: "HH10"},
      {title: "HH02"},
      {title: "HH11"}
]

First I would like to get repeated objects in JSON array like this:

var output = [
     {title: "HH02" },
     {title: "HH08" },
]

Then I would like to get all repeated objects and how many times they are repeated in another JSON array like this

var output = [
     {title: "HH02" , repeat: 3},
     {title: "HH08" , repeat: 2},
]

I tried doing this, but it didn't work well:

data.map(v => v.title).sort().sort((a, b) => {
                    if (a === b) output.push(a);
                })

Possible duplicate of Get list of duplicate objects in an array of objects — Yahiya
– Yahiya, Commented Oct 23, 2019 at 12:16

Code Maniac · Accepted Answer · 2019-10-23 12:07:32Z

2

You can use reduce, filter and map

Group all the values by title first, count there repetition
Filter the titles which appears once or less then once ( exclude them )
map them to get desired output

var data = [{title: "HH02"},{title: "HH03"},{title: "HH04"},{title: "HH02"},{title: "HH07"},{title: "HH08"},{title: "HH08"},{title: "HH10"},{title: "HH02"},{title: "HH11"}]

let final = [...data.reduce((op, inp) => {
  let title = inp.title
  op.set(title, (op.get(title) || 0) + 1)
  return op
}, new Map()).entries()].filter(([_,repeat]) => repeat > 1).map(([title, repeat]) => ({
  title,
  repeat
}))

console.log(final)

edited Oct 23, 2019 at 12:07

answered Oct 23, 2019 at 12:01

Code Maniac

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Comments

Dhilip Kumar · Accepted Answer · 2019-10-23 12:03:28Z

0

You can use lodash groupBy for that.

Here is the link https://lodash.com/docs/4.17.15#groupBy

It will return a JSON object with titles as key and the array of items under that key as its value.

The length of that value will return the required count.

answered Oct 23, 2019 at 12:03

Dhilip Kumar

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Comments

IceMetalPunk · Accepted Answer · 2019-10-23 12:04:08Z

0

I would never suggest having side effects in a sort callback other than sorting the array itself. Try a reduce followed by a filter and map on Object.keys(...):

const countMap = data.reduce((result, element) => {
    result[element.title] = (result[element.title] || 0) + 1;
    return result;
}, {});
const result = Object.keys(countMap).filter(title => countMap[title] > 1).map(title => {
    return {title, repeat: countMap[title]};
});

answered Oct 23, 2019 at 12:04

IceMetalPunk

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Comments

Konrad Słotwiński · Accepted Answer · 2019-10-23 12:35:00Z

0

You can count repeated objects with reduce and filter them out with filter

Object.values(data.reduce((acc, value) => {
  const repeat = acc[value.title] ? acc[value.title].repeat + 1 : 1;
  acc[value.title] = { repeat: repeat, ...value };
  return acc;
}, {})).filter(value => value.repeat > 1);

edited Oct 23, 2019 at 12:35

answered Oct 23, 2019 at 12:02

Konrad Słotwiński

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1 Comment

Andy Over a year ago

You should add some commentary. Code-only answers are not good quality answers.

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