Перетаскиваемая формаГруппы в formArray (реактивные формы)

Вот рабочий пример:

groupDrag.component.ts

import {moveItemInFormArray} from "./move-item-in-form-array";

drop(event: CdkDragDrop<string[]>) {
    moveItemInFormArray(this.arrayControls, event.previousIndex, event.currentIndex);
}

move-item-in-form-array.ts

import {FormArray} from '@angular/forms';

/**
 * Moves an item in a FormArray to another position.
 * @param formArray FormArray instance in which to move the item.
 * @param fromIndex Starting index of the item.
 * @param toIndex Index to which he item should be moved.
 */
export function moveItemInFormArray(formArray: FormArray, fromIndex: number, toIndex: number): void {
  const dir = toIndex > fromIndex ? 1 : -1;

  const from = fromIndex;
  const to = toIndex;

  const temp = formArray.at(from);
  for (let i = from; i * dir < to * dir; i = i + dir) {
    const current = formArray.at(i + dir);
    formArray.setControl(i, current);
  }
  formArray.setControl(to, temp);
}

Это мое рабочее решение

в component.html

    <form [formGroup]="exampleForm">
      <div cdkDropList (cdkDropListDropped)="drop($event)">
        <div formArrayName="formUnits" class="rowGroup"
          *ngFor="let unit of exampleForm.controls.formUnits.controls; let i=index"  
           cdkDrag>
          <div [formGroupName]="i" class="basic-container" cdkDrag>
            <div class="row row-container" >
              <button type="button" class="drag-handle" mat-icon-button cdkDragHandle>
                <mat-icon>unfold_more</mat-icon>
              </button>

              <!-- label input field -->
              <mat-form-field  class="col-lg-4"> 
                <input matInput placeholder="Please enter label without spaces" 
                formControlName="label" required>  
              </mat-form-field>

              <!-- options input field -->
              <mat-form-field  class="col-lg-3"> 
                <input matInput placeholder="Enter Placeholdertext" formControlName="placeholder">
             </mat-form-field>

          </div>
        </div>
      </div>
    </div>
   </form>

в файле component.ts

  drop(event: CdkDragDrop<string[]>) {
    this.formArray = this.exampleForm.get('formUnits') as FormArray;
    const from = event.previousIndex;
    const to = event.currentIndex;
    this.moveItemInFormArray(this.formArray, from, to);
  }

  /**
 * Moves an item in a FormArray to another position.
 * @param formArray FormArray instance in which to move the item.
 * @param fromIndex Starting index of the item.
 * @param toIndex Index to which he item should be moved.
 */
  moveItemInFormArray(formArray: FormArray, fromIndex: number, toIndex: number): void {
    const from = this.clamp(fromIndex, formArray.length - 1);
    const to = this.clamp(toIndex, formArray.length - 1);

    if (from === to) {
      return;
    }

    const previous = formArray.at(from);
    const current = formArray.at(to);
    formArray.setControl(to, previous);
    formArray.setControl(from, current);
  }

  /** Clamps a number between zero and a maximum. */
  clamp(value: number, max: number): number {
    return Math.max(0, Math.min(max, value));
  }