Angular2 ngFor Parent Element

Question

I'm trying to conditionally wrap my bootstrap col-xs-4's three to a row. I have my col-xs-4's rendering fine but i can't figure out how to get them condtionally wrapped in a row. Here is my curren't NgFor:

 <div class="col-xs-4" *ngFor='let linkGroup of linkGroups | siteMapText: siteMapTextFilter; let i=index'>
        <ul class="list-unstyled">
            <li class="heading">
                <div class="clearfix">
                    <span [className]="linkGroup.ContainerCssClass">
                        <span [className]="linkGroup.CssClass"></span>
                    </span>
                    <a href="#">
                        <strong class="heading-text">{{linkGroup.Title}}</strong>
                    </a>
                </div>
            </li>
            <li *ngFor='let link of linkGroup.Links'>
                <a href="#" class="link">
                    <span [className]="link.CssClass"></span>
                    <span class="item">{{link.Title}}</span>
                </a>
            </li>
        </ul>
    </div>

What I would like to do is something like this, but i know its wrong, so what is the right way to do this:

 <div *ngIf='i % 3== 0' class="row">
        <div class="col-xs-4" *ngFor='let linkGroup of linkGroups | siteMapText: siteMapTextFilter; let i=index'>
            <ul class="list-unstyled">
                <li class="heading">
                    <div class="clearfix">
                        <span [className]="linkGroup.ContainerCssClass">
                            <span [className]="linkGroup.CssClass"></span>
                        </span>
                        <a href="#">
                            <strong class="heading-text">{{linkGroup.Title}}</strong>
                        </a>
                    </div>
                </li>
                <li *ngFor='let link of linkGroup.Links'>
                    <a href="#" class="link">
                        <span [className]="link.CssClass"></span>
                        <span class="item">{{link.Title}}</span>
                    </a>
                </li>
            </ul>
        </div>
    </div>

EDIT

The answer was as Gunter suggested, to reorganize the data to be grouped into rows. Then I could organize the template to this:

<div class="row" *ngFor='let linkRow of linkRows| siteMapRowText: siteMapTextFilter'>
    <div class="col-xs-4" *ngFor='let rowCol of linkRow.RowGroups'>
        <ul class="list-unstyled">
            <li class="heading">
                <div class="clearfix">
                    <span [className]="rowCol.ContainerCssClass">
                        <span [className]="rowCol.CssClass"></span>
                    </span>
                    <a href="#">
                        <strong class="heading-text">{{rowCol.Title}}</strong>
                    </a>
                </div>
            </li>
            <li *ngFor='let link of rowCol.Links'>
                <a href="#" class="link">
                    <span [className]="link.CssClass"></span>
                    <span class="item">{{link.Title}}</span>
                </a>
            </li>
        </ul>
    </div>
</div>

Answer 1

Update

You could use a pipe that creates a new array that groups 4 items into an array so you get an array of arrays and then use nested ngFor

@Pipe({ name: 'cols' })
export class ColsPipe implements PipeTransform {
    transform(value: any[], cols: number) {
        var result: any[] = [];
        while(value.length) {
            result.push(value.splice(0, cols));
        }
        return result;
    }
};

See also How to split a long array into smaller arrays, with JavaScript

then use it like

@NgModule({
  declarations: [ColsPipe],
  exports: [ColsPipe]
})
class MySharedModule()

@NgModule({
  imports: [MySharedModule],
  ...
})
class ModuleWhereColsPipeIsUsed {}

@Component({
  selector: '...',
  template: `
  <div class="row" *ngFor='let linkGroupRow of linkGroups | siteMapText: siteMapTextFilter | cols:4; let i=index'>
    <div class="col-xs-4" *ngFor='let linkGroup of linkGroupRow'>...</div>
  </div>
  `
})    

original

This can be achieved using ngTemplateOutlet

At first we create a reusable component:

<template #linkGroupTemplate>
    <div class="col-xs-4">
        <ul class="list-unstyled" let-linkGroup="linkGroup"
                >
            <li class="heading">
                <div class="clearfix">
                    <span [className]="linkGroup.ContainerCssClass">
                        <span [className]="linkGroup.CssClass"></span>
                    </span>
                    <a href="#">
                        <strong class="heading-text">{{linkGroup.Title}}</strong>
                    </a>
                </div>
            </li>
            <li *ngFor='let link of linkGroup.Links'>
                <a href="#" class="link">
                    <span [className]="link.CssClass"></span>
                    <span class="item">{{link.Title}}</span>
                </a>
            </li>
        </ul>
    </div>
</template>

let-linkGroup="linkGroup" declares a context variable linkGroup that refers to the linGroup property of the passed context.

then we use the template inside ngFor and use it wrapped with <div class="row"> on every 4th item, otherwise unwrapped.

<template ngFor let-linkGroup [ngForOf]="linkGroups |siteMapText:siteMapTextFilter" let-i="index">
  <template [ngIf]="i % 3 === 0">
    <div class="row">
     <template [ngTemplateOutlet]="linkGroupTemplate" [ngOutletContext]="{'linkGroup': linkGroup}">
    </div>
  <template>

  <template [ngIf]="i % 3 !== 0">
     <template [ngTemplateOutlet]="linkGroupTemplate" [ngOutletContext]="{'linkGroup': linkGroup}">
  </template>
</template>

<ng-container *ngFor="let linkGroup of linkGroups |siteMapText:siteMapTextFilter" let-i="index">
  <ng-container *ngIf="i % 3 === 0">
    <div class="row">
     <template [ngTemplateOutlet]="linkGroupTemplate" [ngOutletContext]="{'linkGroup': linkGroup}"></template>
    </div>
  <ng-container>

  <ng-container *ngIf="i % 3 !== 0">
     <template [ngTemplateOutlet]="linkGroupTemplate" [ngOutletContext]="{'linkGroup': linkGroup}"></template>
  </ng-container>
</ng-container>

With [ngOutletContext]="{'linkGroup': linkGroup}" we wrap the actual linkGroup value in another object so we can access it as before within the template. Otherwise we would need to declare a variable for each property we want to use

let-CssContainerCssClass="ContainerCssClass" let-CssClass="CssClass" let-Title="Title" let-Links="Links" 

and remove linkGroup. from all bindings.

See also How to repeat a piece of HTML multiple times without ngFor and without another @Component for an example (with Plunker) that uses ngTemplateOutlet and ngOutletContext.