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# Aggregate Operator Predicate Dimension Sample

## About This Sample

This topic describes `AggregateByPredicate.sbapp`, the Aggregate operator predicate dimension sample.

This sample demonstrates use of the predicate-based Aggregate operator. The predicate-based aggregate uses Boolean strings sent to a control port to open, emit from, and close aggregate windows. Data entered on the `TradesIn` port are not processed until true is sent to the `EmitWindow` or `CloseWindow` field of the control port, or both.

The following table lists the predicate expressions entered in the three predicate dimension fields of the Edit Dimension dialog for this sample.

Predicate Field | Expression Entered
--- | ---
Open a window in the current group when | input1.OpenWindow
For windows in the current group, Emit if | input1.EmitWindow || input1.CloseWindow
For windows in the current group, Close if | input1.CloseWindow

The `input1` in these expressions refers to input port 1 of the Aggregate operator. In this sample's case, a Union operator precedes the input port of the Aggregate operator, which combines two input streams, `WindowControl` and `TradesIn`. You send tuples to the `WindowControl` stream to open, emit, or close windows. `OpenWindow`, `EmitWindow`, and `CloseWindow` are all fields of type bool in the schema of the `WindowControl` stream. So you need only send `true` or `false` to one or more of these ports to cause a window control action.

Thus, opening an aggregate window is a matter of sending a tuple containing `true` in the `OpenWindow` field of the `WindowControl` port. With a window open, you can now send tuples to the `TradesIn` stream. However, a computation based on the input trade values is not emitted from the window until you send a tuple containing true to the `EmitWindow` field of the `WindowControl` port.

## Importing This Sample into StreamBase Studio

In StreamBase Studio, import this sample with the following steps:

- From the top-level menu, click File → Load StreamBase Sample.

- Enter `operator` to narrow the list of options.

- Select Operator sample group from the Data Constructs and Operators category.

- Click OK.

StreamBase Studio creates a single project for the all operator samples.

## Running This Sample in StreamBase Studio

1. In the Project Explorer view, open the sample you just loaded.

   If you see red marks on a project folder, wait a moment for the project to load its features.

   If the red marks do not resolve themselves after a minute, select the project, right-click, and select Maven → Update Project from the context menu.

2. Open the `src/main/eventflow/com.tibco.sb.sample.operator` folder.

3. Open the `AggregateByPredicate.sbapp` file and click the Run button. This opens the SB Test/Debug perspective and starts the module.

4. No output is displayed in the Output Streams view yet, but the dequeuer is prepared to receive output. This view will eventually show the output of the application.

5. In the Manual Input view, select the `WindowControl` stream from the Input stream drop-down list.

6. In the `OpenWindow` field, type `true`, then click Send Data.

7. Select `TradesIn` in the Input stream drop-down list.

8. Enter several volume and price pairs, clicking Send Data after each pair. For example, enter Volume=1000, Price=39.45. Make up any pairs of numbers and send them to the application. Notice that no output is showing in the Output Streams view, but you can see the tuples you are sending by switching to the Input Streams view.

9. In the Input stream drop-down, re-select `WindowControl`.

10. Click Clear, then enter `true` in the `EmitWindow` field and click Send Data. Notice that a single tuple now appears in the Output Streams view, showing the calculated VWAP for the volume and price tuples you sent. (Select the tuple to see it in more detail in the Details pane.)

11. Re-select `TradesIn` in the Input stream drop-down list, and send several more pairs of volume and price data.

12. Re-select `WindowControl` in the Input stream drop-down list. Again click Clear, then enter `true` in both the `EmitWindow` and `CloseWindow` fields. Click Send Data. Another tuple displays in the Output Streams view.

13. When done, press F9 or click the Terminate EventFlow Fragment button.

## Sample Location

When you load the sample into StreamBase Studio, Studio copies the sample project's files to your Studio workspace, which is normally part of your home directory, with full access rights.

### Important

Load this sample in StreamBase Studio, and thereafter use the Studio workspace copy of the sample to run and test it, even when running from the command prompt.

Using the workspace copy of the sample avoids permission problems. The default workspace location for this sample is:

    studio-workspace/sample_operator

See Default Installation Directories for the default location of `studio-workspace` on your system.