pandas and xarray allow users to drop part of the dataset with a drop method - see e.g. https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.drop.html. Which is opposite to sel() but should have the same syntax. The drop method should return a new Comparer or ComparerCollection with all data except the dropped.

Two new methods should be added to Comparer and ComparerCollection, respectively, both named drop(). Add them below sel() method