find the index inside formarray in angular for swapping functionality

Inside my formarray i have input fields , i am trying to create a button to swap those field inside the formarray. I want to know how would i find the index of that particular input field

Below is my code

<form [formGroup] ="categoryForm">
                <div formArrayName="categories"
                  *ngFor="let category of categories.controls; let i=index">
                  <div [formGroupName]="i">
                    <div class="form-group row mb-2">
                      <div class="col-md-4">
                        <input class="form-control"
                        id ="{{'categoryName' + i}}"
                        type="text"
                        placeholder="Category Name (required)"
                        formControlName="categoryName"
                        >
                      </div>
    
                      
                      <div class="col-md-1">
                        <button
                          (click)="removeCategory(i)"
                          class="btn btn-danger"
                          style="padding: 5px"
                        >
                      </div>
                      <div class="col-md-1">
                        <button
                          (click)="onSwap(i)"
                          class="btn btn-danger"
                          style="padding: 5px"
                        >
                          SWAP BUTTON
                        </button>
                        &nbsp;&nbsp;
                      </div>

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