I am using angular6 multi-select which have a list of items coming in an array of objects from angular service on ngOnInit like this which is passing into multi-select :
this.sensorTypes = [
  { label : "Power", value : "P"},
  { label : "Current", value : "C"},
  { label : "Voltage", value : "V"}
]
I want to set 2 values by default in multi-select when form will load. For this i am binding ngModel on multi-selectand in that variable i am setting values on ngOnInit like this 
this.selectedAttributes = [
  {label : "Current", value : "C"},
  {label : "Voltage", value : "V"}
]
In my component.html i am creating multi-select like this : 
<div class="form-group row">
  <div class="col-sm-10">
    <ng-select 
       [ngClass]="'ng-select'" 
       [(ngModel)]="selectedAttributes" 
       [ngModelOptions]="{standalone: true}" 
       [options]="sensorTypes"
       [multiple]="true">
    </ng-select>
  </div>
</div>
But values are not setting by default in multi-select.