참조
import {MatRadioModule} from '@angular/material/radio';
@NgModule({
imports: [MatRadioModule]
})
<mat-radio-group (change)="onChangeDifficulty($event)">
<input id="difficulty-easy" type="radio" name="difficulty" value="0" [checked]="difficulty == '0'"><label for="difficulty-easy">Easy</label>
<input id="difficulty-normal" type="radio" name="difficulty" value="1" [checked]="difficulty == '1"><label for="difficulty-normal"> Normal</label>
<input id="difficulty-hard" type="radio" name="difficulty" value="2" [checked]="difficulty == '2'"><label for="difficulty-hard"> Hard</label>
</mat-radio-group>
public onChangeDifficulty(e: any) {
console.log('e.target.value);
}