[angular] How can I limit ngFor repeat to some number of items in Angular?

My Code:

<li *ngFor="let item of list; let i=index" class="dropdown-item" (click)="onClick(item)">
  <template [ngIf]="i<11">{{item.text}}</template>
</li>

I am trying to have only 10 list elements display at any point. As suggested in the answer here, I used ngIf but this results in empty list items (beyond 10) showing up on the page.

This question is related to angular

The answer is


html

<table class="table border">
    <thead>
        <tr>
            <ng-container *ngFor="let column of columns; let i = index">
                <th>{{ column }}</th>
            </ng-container>
        </tr>
    </thead>
    <tbody>
        <tr *ngFor="let row of groups;let i = index">
            <td>{{row.name}}</td>
            <td>{{row.items}}</td>
            <td >
                <span class="status" *ngFor="let item of row.Status | slice:0:2;let j = index">
                    {{item.name}}
                   </span><span *ngIf = "i < 2" class="dots" (mouseenter) ="onHover(i)" (mouseleave) ="onHover(-1)">.....</span> <span [hidden] ="test" *ngIf = "i == hoverIndex" class="hover-details"><span  *ngFor="let item of row.Status;let j = index">
                    {{item.name}}
                   </span></span>
           </td>

        </tr>
  </tbody>
</table>

<p *ngFor="let group of usersg"><input type="checkbox" [checked]="isChecked(group.id)" value="{{group.id}}" />{{group.name}}</p>

<p><select [(ngModel)]="usersr_selected.id">
   <option *ngFor="let role of usersr" value="{{role.id}}">{{role.name}}</option> 
</select></p>

typescript

import { Component, OnInit } from '@angular/core';
import { CommonserviceService } from './../utilities/services/commonservice.service';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';
@Component({
  selector: 'app-home',
  templateUrl: './home.component.html',
  styleUrls: ['./home.component.css']
})
export class HomeComponent implements OnInit {
  getListData: any;
 dataGroup: FormGroup;
 selectedGroups: string[];
    submitted = false;
    usersg_checked:any;
    usersr_selected:any;
    dotsh:any;
    hoverIndex:number = -1;
    groups:any;
    test:any;
 constructor(private formBuilder: FormBuilder) {


     }
     onHover(i:number){
 this.hoverIndex = i;
}
     columns = ["name", "Items","status"];

public usersr = [{
    "id": 1,
    "name": "test1"

}, {
    "id": 2,
    "name": "test2",

}];


  ngOnInit() {
      this.test = false;
      this.groups=[{
        "id": 1,
        "name": "pencils",
        "items": "red pencil",
        "Status": [{
            "id": 1,
            "name": "green"
        }, {
            "id": 2,
            "name": "red"
        }, {
            "id": 3,
            "name": "yellow"
        }],
        "loc": [{
            "id": 1,
            "name": "loc 1"
        }, {
            "id": 2,
            "name": "loc 2"
        }, {
            "id": 3,
            "name": "loc 3"
        }]
    },
    {
        "id": 2,
        "name": "rubbers",
        "items": "big rubber",
        "Status": [{
            "id": 1,
            "name": "green"
        }, {
            "id": 2,
            "name": "red"
        }],
        "loc": [{
            "id": 1,
            "name": "loc 2"
        }, {
            "id": 2,
            "name": "loc 3"
        }]
    },
    {
        "id": 3,
        "name": "rubbers1",
        "items": "big rubber1",
        "Status": [{
            "id": 1,
            "name": "green"
        }],
        "loc": [{
            "id": 1,
            "name": "loc 2"
        }, {
            "id": 2,
            "name": "loc 3"
        }]
    }

];

      this.dotsh = false;

      console.log(this.groups.length);

this.usersg_checked = [{
    "id": 1,
    "name": "test1"

}, {
    "id": 2,
    "name": "test2",

}];

 this.usersr_selected = {"id":1,"name":"test2"};;

this.selectedGroups = [];
this.dataGroup = this.formBuilder.group({
            email: ['', Validators.required]
});
  }

  isChecked(id) {
   console.log(this.usersg_checked);
  return this.usersg_checked.some(item => item.id === id);
}
 get f() { return this.dataGroup.controls; }
onCheckChange(event) {
  if (event.target.checked) {
 this.selectedGroups.push(event.target.value);
} else {
 const index = this.selectedGroups.findIndex(item => item === event.target.value);
 if (index !== -1) {
  this.selectedGroups.splice(index, 1);
}
}
}

   getFormData(value){
      this.submitted = true;

        // stop here if form is invalid
        if (this.dataGroup.invalid) {
            return;
        }
      value['groups'] = this.selectedGroups;
      console.log(value);
  }


}

css

.status{
    border: 1px solid;
    border-radius: 4px;
    padding: 0px 10px;
    margin-right: 10px;
}
.hover-details{
    position: absolute;


    border: 1px solid;
    padding: 10px;
    width: 164px;
    text-align: left;
    border-radius: 4px;
}
.dots{
    position:relative;
}

For example, lets say we want to display only the first 10 items of an array, we could do this using the SlicePipe like so:

<ul>
     <li *ngFor="let item of items | slice:0:10">
      {{ item }}
     </li>
</ul>

This works very well:

<template *ngFor="let item of items; let i=index" >
 <ion-slide *ngIf="i<5" >
  <img [src]="item.ItemPic">
 </ion-slide>
</template>

 <div *ngFor="let item of list;trackBy: trackByFunc" >
   {{item.value}}
 </div>

In your ts file

 trackByFunc(index, item){
    return item ? item.id : undefined;
  }

In addition to @Gunter's answer, you can use trackBy to improve the performance. trackBy takes a function that has two arguments: index and item. You can return a unique value in the object from the function. It will stop re-rendering already displayed items in ngFor. In your html add trackBy as below.

<li *ngFor="let item of list; trackBy: trackByFn;let i=index" class="dropdown-item" (click)="onClick(item)">
  <template [ngIf]="i<11">{{item.text}}</template>
</li>

And write a function like this in your .ts file.

trackByfn(index, item) { 
  return item.uniqueValue;
}

You can directly apply slice() to the variable. StackBlitz Demo

<li *ngFor="let item of list.slice(0, 10);">
   {{item.text}}
</li>