code: public Observable<Page<NamespaceResourceInner>> listByResourceGroupAsync(final String resourceGroupName) {
          return listByResourceGroupWithServiceResponseAsync(resourceGroupName)
              .map(new Func1<ServiceResponse<Page<NamespaceResourceInner>>, Page<NamespaceResourceInner>>() {
                  @Override
                  public Page<NamespaceResourceInner> call(ServiceResponse<Page<NamespaceResourceInner>> response) {
                      return response.body();
                  }
              });
      }
docs: Lists the available namespaces within a resourceGroup.
  
  @param resourceGroupName The name of the resource group. If resourceGroupName value is null the method lists all the namespaces within subscription
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the PagedList&lt;NamespaceResourceInner&gt; object