Removing duplicates with in an object array using angular 4

Question

I have an array with below list of items as shown in image , I would like to remove the duplicates
[L7-LO, %L7-LO] from that array.

I have tried with the following conditions:

Scenario 1 :

this.formulalist.filter((el, i, a) => i == a.indexOf(el))

Scenario 2:

Observable.merge(this.formulalist).distinct((x) => x.Value)
          .subscribe(y => {
       this.formulalist.push(y)
   });

Scenario 3:

this.formulalist.forEach((item, index) => {
        if (index !== this.formulalist.findIndex(i => i.Value == item.Value)) 
        {
            this.formulalist.splice(index, 1);
        }

    });

None of the three scenarios above were able to remove the duplicates from that array. Could any one please help on this query?

Can you provide for us the array and the wanted result? Thank. — Mathias Gheno
– Mathias Gheno, Commented Jan 8, 2019 at 19:11
Your third scenario is somewhat correct, It does not work because findIndex will give the first index, try to loop over the existing array, but populate a new array, do a findIndex in new array. Also, you should not splice the same array you are looping, it will start skipping elements then. — Ashish Ranjan
– Ashish Ranjan, Commented Jan 8, 2019 at 19:19
Possible duplicate of Remove duplicates from an array of objects in JavaScript — David Walschots
– David Walschots, Commented Jan 8, 2019 at 19:55

imperezivan · Accepted Answer · 2019-01-08 19:28:26Z

6

angular is not necessary use vanillajs filter the elements with only one occurrence and add to the new list the first occurrence

let newFormulalist =  formulalist.filter((v,i) => formulalist.findIndex(item => item.value == v.value) === i);

answered Jan 8, 2019 at 19:28

imperezivan

7915 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ashish Ranjan · Accepted Answer · 2020-09-08 08:08:49Z

Try populating a new array without duplicates. Assign the new array later to formulalist.

newArr = []
this.formulalist.forEach((item, index) => {
    if (this.newArr.findIndex(i => i.Value == item.Value) === -1) 
    {
        this.newArr.push(item)
    }

});
this.formulalist = this.newArr

EDIT

Looking at the answer above, the solution seems so outdated. A better approach would have been to use an Array.filter() than a Array.forEach().

But, having a better solution would be nice, now when I see this question, I feel findIndex() not to be a good approach because of the extra traversal.

I may have a Set and store the values in the Set on which I want to filter, If the Set has those entries, I would skip those elements from the array.

Or a nicer approach is the one that is used by Akitha_MJ, very concise. One loop for the array length, an Object(Map) in the loop with keys being the value on which we want to remove duplicates and the values being the full Object(Array element) itself. On the repetition of the element in the loop, the element would be simply replaced in the Map. Later just take out the values from the Map.

Akitha_MJ · Accepted Answer · 2020-01-03 08:42:39Z

3

const result = Array.from(this.item.reduce((m, t) => m.set(t.name, t), new Map()).values());

Hope this works !!

answered Jan 3, 2020 at 8:42

Akitha_MJ

4,30429 silver badges20 bronze badges

Comments

Keyur Patel · Accepted Answer · 2021-05-08 20:53:38Z

2

// user reduce method to remove duplicates from object array , very easily

  this.formulalist= this.formulalist.reduce((a, b) => {
      if (!a.find(data => data.name === b.name)) {
        a.push(b);
      }
      return a;
    }, []);

// o/p = in formulalist you will find only unique values

answered May 8, 2021 at 20:53

Keyur Patel

671 gold badge1 silver badge5 bronze badges

1 Comment

Pawara Siriwardhane Over a year ago

Welcome to Stack Overflow. While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply.

quirimmo · Accepted Answer · 2019-01-08 19:31:56Z

0

Use a reducer returning a new array of the unique objects:

const input = [{
    value: 'L7-LO',
    name: 'L7-LO'
  },
  {
    value: '%L7-LO',
    name: '%L7-LO'
  },
  {
    value: 'L7-LO',
    name: 'L7-LO'
  },
  {
    value: '%L7-LO',
    name: '%L7-LO'
  },
  {
    value: 'L7-L3',
    name: 'L7-L3'
  },
  {
    value: '%L7-L3',
    name: '%L7-L3'
  },
  {
    value: 'LO-L3',
    name: 'LO-L3'
  },
  {
    value: '%LO-L3',
    name: '%LO-L3'
  }
];
console.log(input.reduce((acc, val) => {
  if (!acc.find(el => el.value === val.value)) {
    acc.push(val);
  }
  return acc;
}, []));

edited Jan 8, 2019 at 19:31

answered Jan 8, 2019 at 19:24

quirimmo

10k3 gold badges33 silver badges46 bronze badges

Comments

Piyush Khanna · Accepted Answer · 2019-01-08 19:55:43Z

0

if you are working using ES6 and up, basic JS using map and filter functions makes it easy.

var array = [{value:"a"},{value:"b"},{value:"c"},{value:"a"},{value:"c"},{value:"d"}];

console.log(array.filter((obj, pos, arr) => {
    return arr.map(mapObj => mapObj["value"]).indexOf(obj["value"]) === pos;
}));

answered Jan 8, 2019 at 19:55

Piyush Khanna

2962 silver badges14 bronze badges

Comments

Dasha Ermolova · Accepted Answer · 2019-01-08 20:07:21Z

0

Filtering for unique values is much faster with assigning values to some object properties - there not will be duplicates. This approach gets better and better with every +1 member of initial array, because looping will be causing fast algorithm complications

let arr = [
  {value: 'L7-LO', name: 'L7-LO'},
  {value: '%L7-LO', name: '%L7-LO'},
  {value: 'L7-LO', name: 'L7-LO'},
  {value: '%L7-LO', name: '%L7-LO'},
  {value: 'L7-L3', name: 'L7-L3'},
  {value: '%L7-L3', name: '%L7-L3'},
  {value: 'LO-L3', name: 'LO-L3'},
  {value: '%LO-L3', name: '%LO-L3'}
];
let obj = {};

const unique = () => {
  let result = [];
  
  arr.forEach((item, i) => {
    obj[item['value']] = i;
  });
  
  for (let key in obj) {
    let index = obj[key];
    result.push(arr[index])
  }
  
  return result;
}

arr = unique(); // for example; 

console.log(arr);

edited Jan 8, 2019 at 20:07

answered Jan 8, 2019 at 19:28

Dasha Ermolova

5544 silver badges6 bronze badges

3 Comments

Glory Raj Over a year ago

Could you please update on How to reassign the result back to formula list.

Dasha Ermolova Over a year ago

unique() - is a function, that returns a new array with "filtered" values from the initial one. But you have quite a large room for manoeuvre

Dasha Ermolova Over a year ago

the main idea is to 1) loop just once and store the array item and index in a key-value pair of some auxiliary object 2) after that you have no duplicates for sure, because object can't have 2 absolutely the same property names, it overrides the repeating ones

Collectives™ on Stack Overflow

Removing duplicates with in an object array using angular 4

7 Answers 7

Comments

Comments

Comments

1 Comment

Comments

Comments

3 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

Comments

Comments

1 Comment

Comments

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related