How to apply filters to *ngFor?

Question

Apparently, Angular 2 will use pipes instead of filters as in Angular1 in conjunction with ng-for to filter results, although the implementation still seems to be vague, wit

Answer 1

Another approach I like to use for application specific filters, is to use a custom read-only property on your component which allows you to encapsulate the filtering logic more cleanly than using a custom pipe (IMHO).

For example, if I want to bind to albumList and filter on searchText:

searchText: "";
albumList: Album[] = [];

get filteredAlbumList() {
    if (this.config.searchText && this.config.searchText.length > 1) {
      var lsearchText = this.config.searchText.toLowerCase();
      return this.albumList.filter((a) =>
        a.Title.toLowerCase().includes(lsearchText) ||
        a.Artist.ArtistName.toLowerCase().includes(lsearchText)
      );
    }
    return this.albumList;
}

To bind in the HTML you can then bind to the read-only property:

<a class="list-group-item"
       *ngFor="let album of filteredAlbumList">
</a>

I find for specialized filters that are application specific this works better than a pipe as it keeps the logic related to the filter with the component.

Pipes work better for globally reusable filters.

Answer 2

For this requirement, I implement and publish a generic component. See

https://www.npmjs.com/package/w-ng5

For use this components, before, install this package with npm:

npm install w-ng5 --save

After, import module in app.module

...
import { PipesModule } from 'w-ng5';

In the next step, add in declare section of app.module:

imports: [
  PipesModule,
  ...
]

Sample use

Filtering simple string

<input type="text"  [(ngModel)]="filtroString">
<ul>
  <li *ngFor="let s of getStrings() | filter:filtroString">
    {{s}}
  </li>
</ul>

Filtering complex string - field 'Value' in level 2

<input type="text"  [(ngModel)]="search">
<ul>
  <li *ngFor="let s of getComplexTypesExtends() | filter:[{field:'n1.n2.valor2', value: search}]">
    {{s.nome}} - {{s.idade}} - {{s.n1.valor1}} - {{s.n1.n2.valor2}}
  </li>
</ul>

Filtering complex string - middle field - 'Value' in level 1

<input type="text"  [(ngModel)]="search3">
<ul>
  <li *ngFor="let s of getComplexTypesExtends() | filter:[{field:'n1.valor1', value: search3}]">
    {{s.nome}} - {{s.idade}} - {{s.n1.valor1}} - {{s.n1.n2.valor2}}
  </li>
</ul>

Filtering complex array simple - field 'Nome' level 0

<input type="text"  [(ngModel)]="search2">
<ul>
  <li *ngFor="let s of getComplexTypesExtends() | filter:[{field:'nome', value: search2}]">
    {{s.nome}} - {{s.idade}} - {{s.n1.valor1}} - {{s.n1.n2.valor2}}
  </li>
</ul>

Filtering in tree fields - field 'Valor' in level 2 or 'Valor' in level 1 or 'Nome' in level 0

<input type="text"  [(ngModel)]="search5">
<ul>
  <li *ngFor="let s of getComplexTypesExtends() | filter:[{field:'n1.n2.valor2', value: search5}, {field:'n1.valor1', value: search5}, {field:'nome', value: search5}]">
    {{s.nome}} - {{s.idade}} - {{s.n1.valor1}} - {{s.n1.n2.valor2}}
  </li>
</ul>

Filtering nonexistent field - 'Valor' in nonexistent level 3

<input type="text"  [(ngModel)]="search4">
<ul>
  <li *ngFor="let s of getComplexTypesExtends() | filter:[{field:'n1.n2.n3.valor3', value: search4}]">
    {{s.nome}} - {{s.idade}} - {{s.n1.valor1}} - {{s.n1.n2.valor2}}
  </li>
</ul>

This component work with infinite attribute level...

Answer 3

I've created a plunker based off of the answers here and elsewhere.

Additionally I had to add an @Input, @ViewChild, and ElementRef of the <input> and create and subscribe() to an observable of it.

Angular2 Search Filter: PLUNKR (UPDATE: plunker no longer works)

Answer 4

You could also use the following:

<template ngFor let-item [ngForOf]="itemsList">
    <div *ng-if="conditon(item)"></div>
</template>

This will only show the div if your items matches the condition

See the angular documentation for more information If you would also need the index, use the following:

<template ngFor let-item [ngForOf]="itemsList" let-i="index">
    <div *ng-if="conditon(item, i)"></div>
</template>

Answer 5

This is my code:

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

@Pipe({
    name: 'filter'
})
@Injectable()
export class FilterPipe implements PipeTransform {
    transform(items: any[], field : string, value): any[] {
      if (!items) return [];
      if (!value || value.length === 0) return items;
      return items.filter(it =>
      it[field] === value);
    }
}

Sample:

LIST = [{id:1,name:'abc'},{id:2,name:'cba'}];
FilterValue = 1;

<span *ngFor="let listItem of LIST | filter : 'id' : FilterValue">
                              {{listItem .name}}
                          </span>

Answer 6

Here's an example that I created a while back, and blogged about, that includes a working plunk. It provides a filter pipe that can filter any list of objects. You basically just specify the property and value {key:value} within your ngFor specification.

It's not a lot different from @NateMay's response, except that I explain it in relatively verbose detail.

In my case, I filtered an unordered list on some text (filterText) the user entered against the "label" property of the objects in my array with this sort of mark-up:

<ul>
  <li *ngFor="let item of _items | filter:{label: filterText}">{{ item.label }}</li>
</ul>

https://long2know.com/2016/11/angular2-filter-pipes/