Angular – How to mat-button-toggle by default selected in angular

You need to assign each button a value and then you can give the group an initial value (matching one of the buttons);

<md-button-toggle-group #group="mdButtonToggleGroup" value="button1">
    <md-button-toggle value="button1">
      <span>one</span>
    </md-button-toggle>
    <md-button-toggle value="button2">
      <span>second</span>
    </md-button-toggle>
  </md-button-toggle-group>

Use a binding for the value in your template.

value="{{ option.id }}"

should be

[value]="option.id"

And in your selected value use ngModel instead of value.

<mat-select [(value)]="selected2">

should be

<mat-select [(ngModel)]="selected2">

Complete code:

<div>
  <mat-select [(ngModel)]="selected2">
    <mat-option *ngFor="let option of options2" [value]="option.id">{{ option.name }}</mat-option>
  </mat-select>
</div>

On a side note as of version 2.0.0-beta.12 the material select now accepts a mat-form-field element as the parent element so it is consistent with the other material input controls. Replace the div element with mat-form-field element after you upgrade.

<mat-form-field>
  <mat-select [(ngModel)]="selected2">
    <mat-option *ngFor="let option of options2" [value]="option.id">{{ option.name }}</mat-option>
  </mat-select>
</mat-form-field>