CODEWITHSUNDEEP
angularngfor
dota2pro
dota2pro

Reputation: 7856

Simple pipe to reverse array items in ngFor Angular 8+ without changing array index?

How Can i reverse without changing positions of elements in an array, should just update the view with a pipe

I can use array.reverse() but that places the first item at the last and so on so elements index changes

Here is stackblitz code which I am stuck at 

    import { Component } from '@angular/core';

export interface Order {
  value: string;
  viewValue: string;
}

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

@Pipe({
  name: 'orderBy'
})
export class OrderByPipe implements PipeTransform {

  transform(value: any[], arg: string): any {
    console.log('value', value);
    console.log('args', arg);

    if (arg === 'desc') {
      return value.reverse();
    }

    if (arg === 'asc') {
      return value;
    }
  }

}

/**
 * @title Basic select
 */
@Component({
  selector: 'select-overview-example',
  template: `<h4>Basic mat-select</h4>
<mat-form-field>
    <mat-label>Sort Order</mat-label>
    <mat-select value='asc'>
        <mat-option *ngFor="let order of orders" (click)="changeOrder(order.value)" [value]="order.value">
            {{order.viewValue}}
        </mat-option>
    </mat-select>
</mat-form-field>


<ul>
    <li *ngFor="let item of items| orderBy : sort; index as i">{{i}} -> {{item}}</li>
</ul>`,
  styleUrls: ['select-overview-example.css'],
})
export class SelectOverviewExample {
  orders: Order[] = [
    { value: 'asc', viewValue: 'Ascending' },
    { value: 'desc', viewValue: 'Descending' }
  ];

  items: number[] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  sort: string = 'asc';

  changeOrder(val: string) {

    console.log('val', val);

    this.sort = val;
  }

}

Upvotes: 2

Views: 5111

Answers (3)

Mayur Kukadiya
Mayur Kukadiya

Reputation: 2747

Our main problem is to change view only in reverse order. so no need to update logic. only update CSS.

If items are display using flex-box CSS, then we can reverse it by using flex-direction property.

    flex-direction : row;
    flex-direction: column;
    flex-direction: row-reverse;
    flex-direction: column-reverse;

and if items are display using UL and LI, then apply below css for reverse Order. like below :

ul {
-moz-transform: rotate(180deg);
-webkit-transform: rotate(180deg);
transform: rotate(180deg);
}
ul > li {
    -moz-transform: rotate(-180deg);
    -webkit-transform: rotate(-180deg);
    transform: rotate(-180deg);
}

Upvotes: 4

adamdport
adamdport

Reputation: 12613

You can clone your array using let clone = myArray.slice();. Reordering the clone will not impact the original array. It looks like that's what Material's table does.

Upvotes: 0

Roliver Javier
Roliver Javier

Reputation: 44

You can make a custom pipe for sorting asc or desc and sort your array

##TEMPLATE##
<div *ngFor="let order of Orders | orderBy:'asc'">

##PIPE##
export class OrderByPipe  implements PipeTransform {
transform(orders: any[], field: string): any[] {
    orders.sort((a: any, b: any) => {
    if (a[field] < b[field]) {
     return -1;
    } else if (a[field] > b[field]) {
      return 1;
    } else {
        return 0;
    }
    });
    }
}

Upvotes: 0

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