Using the Filter Operator

The Filter operator accepts a single Input Stream and applies one or more predicates (tests) to the arriving tuples. A predicate returns TRUE or FALSE. If a tuple's data matches a TRUE condition in a predicate, it is moved onto a designated output stream. You can define a Filter operator so that tuples not matching any of the predicates are either dropped or sent to an output stream.

Use the Filter operator when you want to choose different processing of data depending on some characteristic of the data. For example, if you wanted to create an alert if a stock trade transaction exceeded a specified number of shares, then use a predicate such as numShares > threshold to send those tuples to a stream to do the alert.

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The Predicate Settings tab allows you to specify one or more predicates (tests) to apply to the arriving tuples. A predicate returns TRUE or FALSE. If a tuple's data matches a TRUE condition in a predicate, it is moved onto a designated output stream.

Each predicate is a test to be performed on the input tuple. Predicates are evaluated in the order in which they appear. If the predicate evaluates to TRUE, the tuple is sent to the corresponding output stream; if not, the next predicate is evaluated. A tuple is sent only to the first stream whose predicate is matched. If the Create Output Port for Non-matching Tuples option is checked and no other expressions return TRUE, the tuple is sent to an additional output port. If this option is not selected, no tuple is emitted.

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