Angular Material mat-table Row Grouping

A very simple answer would be to sort by the GroupID, this will put those rows together in groups. However, I'm guessing you want a header row displayed before each group.

You can provide an alternative <mat-row *matRowDef="... that uses a where clause. This can be used to display a non-default set of columns. The where clause takes a function that returns true if that matRowDef should be used.

The data you supply to the table would then be the data rows interspersed with group rows, and the function tells one from the other. Taking Basic use of <table mat-table> as a starter, manually add the groups and add the where clause function to app/table-basic-example.ts:

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

    export interface PeriodicElement {
      name: string;
      position: number;
      weight: number;
      symbol: string;
    }

    export interface Group {
      group: string;
    }

    const ELEMENT_DATA: (PeriodicElement | Group)[] = [
      {group: "Group 1"},
      {position: 1, name: 'Hydrogen', weight: 1.0079, symbol: 'H'},
      {position: 2, name: 'Helium', weight: 4.0026, symbol: 'He'},
      {position: 3, name: 'Lithium', weight: 6.941, symbol: 'Li'},
      {position: 4, name: 'Beryllium', weight: 9.0122, symbol: 'Be'},
      {group: "Group 2"},
      {position: 5, name: 'Boron', weight: 10.811, symbol: 'B'},
      {position: 6, name: 'Carbon', weight: 12.0107, symbol: 'C'},
      {position: 7, name: 'Nitrogen', weight: 14.0067, symbol: 'N'},
      {group: "Group 3"},
      {position: 8, name: 'Oxygen', weight: 15.9994, symbol: 'O'},
      {position: 9, name: 'Fluorine', weight: 18.9984, symbol: 'F'},
      {position: 10, name: 'Neon', weight: 20.1797, symbol: 'Ne'},
    ];

    /**
     * @title Basic use of `<table mat-table>`
     */
    @Component({
      selector: 'table-basic-example',
      styleUrls: ['table-basic-example.css'],
      templateUrl: 'table-basic-example.html',
    })
    export class TableBasicExample {
      displayedColumns: string[] = ['position', 'name', 'weight', 'symbol'];
      dataSource = ELEMENT_DATA;

      isGroup(index, item): boolean{
        return item.group;
      }
    }


    /**  Copyright 2018 Google Inc. All Rights Reserved.
        Use of this source code is governed by an MIT-style license that
        can be found in the LICENSE file at http://angular.io/license */

And add the groupHeader Column and the extra matRowDef to the app/table-basic-example.html:

    <mat-table [dataSource]="dataSource" class="mat-elevation-z8">

      <!--- Note that these columns can be defined in any order.
            The actual rendered columns are set as a property on the row definition" -->

      <!-- Position Column -->
      <ng-container matColumnDef="position">
        <mat-header-cell *matHeaderCellDef> No. </mat-header-cell>
        <mat-cell *matCellDef="let element"> {{element.position}} </mat-cell>
      </ng-container>

      <!-- Name Column -->
      <ng-container matColumnDef="name">
        <mat-header-cell *matHeaderCellDef> Name </mat-header-cell>
        <mat-cell *matCellDef="let element"> {{element.name}} </mat-cell>
      </ng-container>

      <!-- Weight Column -->
      <ng-container matColumnDef="weight">
        <mat-header-cell *matHeaderCellDef> Weight </mat-header-cell>
        <mat-cell *matCellDef="let element"> {{element.weight}} </mat-cell>
      </ng-container>

      <!-- Symbol Column -->
      <ng-container matColumnDef="symbol">
        <mat-header-cell *matHeaderCellDef> Symbol </mat-header-cell>
        <mat-cell *matCellDef="let element"> {{element.symbol}} </mat-cell>
      </ng-container>

      <ng-container matColumnDef="groupHeader">
        <mat-cell *matCellDef="let group">{{group.group}}</mat-cell>
      </ng-container>

      <mat-header-row *matHeaderRowDef="displayedColumns"></mat-header-row>
      <mat-row *matRowDef="let row; columns: displayedColumns"></mat-row>
      <mat-row *matRowDef="let row; columns: ['groupHeader']; when: isGroup"> </mat-row>

    </mat-table>



    <!-- Copyright 2018 Google Inc. All Rights Reserved.
        Use of this source code is governed by an MIT-style license that
        can be found in the LICENSE file at http://angular.io/license -->

Here is a finished stackblitz which groups by the element's initial letter.

And here is a far more developed stackblitz just supply the list of columns you want to group by and it will insert the group rows for you. You can also click the group rows to expand or collapse them

And finally here is a Github project that modifies a copy of the MatTableDataSource class from the material codebase. Works nicely with filter and sort, but 'competes' with the paginator as they both limit the view of records in different ways.

Using Stephen Turner's answer, now sharing this stackblitz fork that

  • Dynamicaly discovers columns in the given data
  • Allows to groupby distinct values of the columns on demand

As it was pointed out earlier in this thread,

the easy way to groupBy with Mat-Table is in practice to add rows in the displayed data,

these lines added on start of each new group can be given a custom template with the @Input(matRowDefWhen)

<!-- Default Table lines -->
<tr mat-header-row *matHeaderRowDef="displayedColumns; sticky: true"></tr>
<tr mat-row *matRowDef="let row; columns: displayedColumns;"></tr>

<!-- Group line -->
<tr mat-row *matRowDef="let row; columns: ['groupName']; when: isAGroup"></tr>

In the above example the isAGroup function should return true when a line is a group and not part of the initial data.

Also the groupName column template could be implemented as follows

<ng-container matColumnDef="groupName">
    <td colspan="999" mat-cell *matCellDef="let group">
      {{group.name}}
    </td>
</ng-container>

Finally, if your dataset can vary one could be adding a loop on column template definitions

<ng-container *ngFor="let col of displayedColumns" [matColumnDef]="col">
    <th mat-header-cell *matHeaderCellDef>{{ col }}</th>
    <td mat-cell *matCellDef="let row">{{ row[col] }}</td>
</ng-container>

then hidding and showing the group's lines is just a matter of filtering the displayed data based on the newly hidden group criteria and refreshing the displayed data.

Sorry for this thread necro, only aiming at sharing a piece of reusable code to those looking for a solution.