Deleting attributes with a single valid value

Removing attributes where one or more of the examples are missing is easy using the "Select Attributes" operator with the option "no missing values".

If however, you want to additionally remove attributes where only a single example is valid and all the rest are missing, a neat way to do this is to use the "Remove Useless Attributes" operator. One of the parameters to this is "numerical min deviation" and this will remove any attribute with a deviation less than or equal to the value supplied which defaults to 0. Attributes with only a single valid value will have a deviation of 0 and will therefore be removed by this operator.