OPAL Filter Verbs

Filter verbs select particular rows from the input row set, emitting the matches as output.

Verb	Description
always	When the verb input is a Resource dataset, always selects all resources that matched the predicate at all times.
bottomk	Selects all data for each of the bottom k ranked groups.
ever	When the verb input is a Resource dataset, ever selects all resources that at some point matched the predicate.
filter	Exclude rows from the input dataset that do not match the given predicate expression.
filter_last	Exclude rows from the input dataset that do not match the given predicate expression.
limit	Select the first count rows based on the current ordering of the input and filter out the rest.
never	When the verb input is a Resource dataset, never selects all resources that at no point matched the predicate.
topk	Selects all data for each of the top k ranked groups.