Find duplicate values by key from array of objects in Javascript

Question

I know this question was answered before multiple times. but i didn't find any solution that helped me out.

I got an array of objects with a Name property. I only want to get the objects with the same name.

How my Array looks like:

[
  {
    Name: 'test',
    coolProperty: 'yeahCool1'
  },
  {
    Name: 'test1',
    coolProperty: 'yeahCool2'
  },
  {
    Name: 'test2',
    coolProperty: 'yeahCool3'
  },
  {
    Name: 'test3',
    coolProperty: 'yeahCool4'
  },
  {
    Name: 'test',
    coolProperty: 'yeahCool5'
  }
]

so I only want to get:

[
  {
    Name: 'test',
    coolProperty: 'yeahCool1'
  },
  {
    Name: 'test',
    coolProperty: 'yeahCool5'
  }
]

I hope someone can help me out :)

CertainPerformance · Accepted Answer · 2018-08-23 08:39:42Z

1

For an O(N) solution, first reduce the array into an object that counts the number of occurrences of each name, and then filter the input by the occurrence count being 2:

const arr = [
  {
    Name: 'test',
    coolProperty: 'yeahCool1'
  },
  {
    Name: 'test1',
    coolProperty: 'yeahCool2'
  },
  {
    Name: 'test2',
    coolProperty: 'yeahCool3'
  },
  {
    Name: 'test3',
    coolProperty: 'yeahCool4'
  },
  {
    Name: 'test',
    coolProperty: 'yeahCool5'
  }
];
const counts = arr.reduce((a, { Name }) => {
  a[Name] = (a[Name] || 0) + 1;
  return a;
}, {});
console.log(arr.filter(({ Name }) => counts[Name] === 2));

answered Aug 23, 2018 at 8:39

CertainPerformance

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2 Comments

newbieTwoPointOH Over a year ago

it works with my fake data sample but doesnt with my real data: jsfiddle.net/hrpg2qy3 why is that?

CertainPerformance Over a year ago

@newbieTwoPointOH If you wanted the three Marktanalyses, then filter by the count being 3 instead of 2 (or >= 2 instead of === 2)

Narendra Jadhav · Accepted Answer · 2018-08-23 09:09:07Z

0

You could use reduce() and filter() method to get the required result.

Using filter() method you need to check if length is greater than 2 then need it will be push in new array inside of reduce() method

DEMO

const arr =[{"Name":"test","coolProperty":"yeahCool1"},{"Name":"test1","coolProperty":"yeahCool2"},{"Name":"test2","coolProperty":"yeahCool3"},{"Name":"test3","coolProperty":"yeahCool4"},{"Name":"test","coolProperty":"yeahCool5"}];

let getCount = (name)=>{
  return arr.filter(o => o.Name == name).length;
}

console.log(arr.reduce((r,item) => {
  let len = getCount(item.Name);
  return r.concat(len>1?item:[]);
}, []));

answered Aug 23, 2018 at 9:09

Narendra Jadhav

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Comments

Nimeshka Srimal · Accepted Answer · 2018-08-23 11:26:09Z

0

I see that you have already got an answer. So I thought of adding another way using map.

var counts = {};

var repeats = {};
arr.map(i => {
    counts[i['Name']] = (counts[i['Name']] || []);
    counts[i['Name']].push(i);

    if (counts[i['Name']].length > 1) {
        repeats[i['Name']] = counts[i['Name']];
    }
});

console.log(repeats);

Not the best solution considering the performance. Just wanted to add an alternative method.

Hope it helps!!

edited Aug 23, 2018 at 11:26

answered Aug 23, 2018 at 9:27

Nimeshka Srimal

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