Filter unique elements from array using Pipe filter in Angular

Question

I am trying to implement pipes using Angular. Below is the code I have tried. I want to retrieve unique for the complete list . So i have added a pipe filter name for the inner list . But i am still getting the duplicate elements. I have added the json for reference .The inner ArticleTags array has a list of objects. Similarly I have multiple ArticleTags array for every parent Array. I want to retrieve the unique elements from the entire list ArticleTags array. I think its retrieving the unique elements within the particular inner list and not retrieving from the entire list of Article Tags.

import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
    name: 'filterUnique',
    pure: false
  })
  export class FilterPipe implements PipeTransform {
    transform(value: any, args?: any): any {
      // Remove the duplicate elements
      const uniqueArray = value.filter(function (el, index, array) {
        return array.indexOf (el) === index;
      });
      return uniqueArray;
    }
  }







<ul>
          <li *ngFor="let articlesResult of articlesListArray; let i=index">
            <ul>
              <li  *ngFor="let articlesTagResult of articlesResult.ArticleTags | filterUnique; let j=index">
                <i class="fa fa-times-circle" *ngIf="articlesResult.ArticleTags[j].value"></i>
                <label class="form-check-label" for="exampleCheck" *ngIf="articlesResult.ArticleTags[j].value">{{articlesResult.ArticleTags[j].value}}</label>
              </li>
            </ul>
          </li>
        </ul>


getLatestArticles(currdate): void {
    this.ng4LoadingSpinnerService.show();
    this.ArticlesServiceCall.getArticlesDashboard(currdate)
      .subscribe(
        resultArray => {
          this.ng4LoadingSpinnerService.hide();
          this.articlesList = resultArray;
          this.articlesLists = resultArray.ResponseValue;
          this.articlesListArray = this.articlesLists.slice(0, 8);
        },
        error => console.log('Error :: ' + error)
      );
  }

I am getting the main array data from articlesListArray and passing that in html

---

Edit update on July 09 2018

Getting the below error with the below pipe code.

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({ name: 'filterduplicates' }) export class FilterduplicatesPipe implements PipeTransform {

transform(value: any, args?: any): any {
    // Remove the duplicate elements
    const art = value.map( x => {
        return x.ArticleTags ? x.ArticleTags.map(y => {
            return y.value ? y.value : null;
        }) : [];
    }).reduce((acc, ele, i) => {
        acc = acc.concat(ele);
        return acc;
    }).filter( z => {
        if (z) {
            return z;
        }
    });
    return new Set(art);
}

}

Solution 1

Assuming your article[] is like so:

articles = [
    {
        ArticleTitle: 'article one',
        ArticleTags: [
            {key:0, value:'Back'},
            {key:1, value:'Shoulder'},
            {key:2, value:'Injury'},
            {key:3, value:'Abs'}]
    },
    {
        ArticleTitle: 'article two',
        ArticleTags: [
            {key:3, value:'Abs'},
            {key:1, value:'Shoulder'},
            {key:4, value:'Leg'},
            {key:5, value:'Others'}]}
]


import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
    name: 'filterUnique',
    pure: false
})
export class FilterPipe implements PipeTransform {
    transform(value: any, args?: any): any {
        // Remove the duplicate elements
        var art = value.map(x=>{
            return x.ArticleTags.map(y=>{ return y.value;});;
        }).reduce((acc,ele,i)=>{
            acc = acc.concat(ele);
            return acc;
        });
        return new Set(art);
    }
}

above pipe returns a set of string containing the value of articletag.

<ul>
    <li *ngFor="let a of articles | filterUnique">{{a}}</li>
</ul>

Solution 2

Refere this there unique filter is given https://www.npmjs.com/package/ng2-pipes

  ex:   array | unique: 'Property (Optional)'
        this.items = [1, 2, 3, 1, 2, 3];
        <li *ngFor="let item of items | unique"> <!-- Array: [1, 2, 3] -->

Comments

[j4rey]

so you are looping through articlesListArray to get articlesResult, then in second <li> tag you are looping through articlesResult.ArticleTags to get unique articlesTagResult, but instead of using articlesTagResult.value, you are using articlesResult.ArticleTags[j].value?

[Nancy]

Okay so i tried to use <label class="form-check-label" for="exampleCheck">{{articlesTagResult.value}}</label> but still it retrieves the duplicate elements . I have also attached the screen shot of output for your reference . The second array is a list of elements. Back, Injury ,Lifestyle , Shoulder comes under one list. As per my assumption , it is retrieving the unique elements with in that array. But it doesnt compare with other list of array elements, or I am not sure .

[j4rey]

okay i get it now, you have list of articles, every articles has tags, and you want the union of tags of all articles....right?

[Nancy]

Yes you are exactly right

[Nancy]

@ j4rey89 Any clue on this how to achieve from .ts file . I have pasted .ts code for reference.

[Nancy]

@j4rey89 stackoverflow.com/questions/50897124/… Can you take a look at this question .

[Soumya B. Athani]

ok, then try to use sets in angular to your response from server it will display only unique elements

[Nancy]

I have already done all those. My requirement is well understood by j4rey89 as he had mentioned in his comment.

[Sanoj_V]

can you try to inject in your component @Component({ pipes: [FilterPipe] }) try this also.

[Nancy]

I used the code in pipe file and getting error Cannot read property 'map' of undefined . Could you please remove the repetitive code from your answer and have a single answer . I see there are lots of repetitions. However, I get the above error with the code that you had mentioned in pipe file.

[j4rey]

removed the repetitive code.....As for Cannot read property 'map' of undefined, map is a property of Array make sure the data is of type Array.

[Nancy]

Actually I am getting the list of unique elements displayed :) , but with the error message Cannot read property 'map' of undefined, map is a property of Array in console :( But still I am accepting your answer.

[j4rey]

kindly check the green tick, if my answer helped solved your problem.

[Nancy]

I have done. .But do you know why i am getting that error although I am getting the correct unique list?

[j4rey]

could you provide the complete json data that you are setting in articlesListArray?

[Nancy]

Have another query . I have this cross icon as shown in the above image for every article tag. When i click on the icon , that particular tag should be removed from the list . How to achieve this after retrieving the unique list of elements ? I tried to use splice but deletion of that particular alone is not happening. For me it deleted that specific list completely.

[j4rey]

@Nancy I am afraid you will have to create another question for that since it's a different issue.

[Nancy]

I am getting map error with the code mentioned above. I have updated the question with error message screen shot and the pipe code. Could you pls help

[j4rey]

check if articles has values and is of type array using Array.isArray(obj).