Growing and Pruning the Tree

To launch the tree builder, execute a stream containing a C&R Tree, QUEST, or CHAID node, making sure the Launch interactive session option is selected on the Objectives panel of the Build Options tab.

The Viewer tab in the tree builder enables you to view the current tree, starting with the root node.

1. To grow the tree, from the menus choose:

   Tree > Grow Tree

   The system builds the tree by recursively splitting each branch until one or more stopping criteria are met. At each split, the best predictor is automatically selected based on the modeling method used.

2. Alternatively, select Grow Tree One Level to add a single level.
3. To add a branch below a specific node, select the node and select Grow Branch.
4. To choose the predictor used for a split, select the desired node and select Grow Branch with Custom Split. See the topic Defining Custom Splits for more information.
5. To prune a branch, select a node and select Remove Branch to clear up the selected node.
6. To remove the bottom level from the tree, select Remove One Level.
7. For C&R Tree and QUEST trees only, select Grow Tree and Prune to prune based on a cost-complexity algorithm that adjusts the risk estimate based on the number of terminal nodes, typically resulting in a simpler tree. See the topic C&R Tree Node for more information.

Reading Split Rules on the Viewer Tab

When viewing split rules on the Viewer tab, square brackets mean that the adjacent value is included in the range whereas parentheses indicate that the adjacent value is excluded from the range. The expression (23,37] therefore means from 23 exclusive to 37 inclusive; that is, from just above 23 to 37. On the Model tab, the same condition would be displayed as:

Age > 23 and Age <= 37

Interrupting tree growth. To interrupt a tree-growing operation (if it is taking longer than expected, for example), click the Stop Execution button on the toolbar.

Figure 1. Stop Execution button

The button is enabled only during tree growth. It stops the current growing operation at its current point, leaving any nodes that have already been added, without saving changes or closing the window. The tree builder remains open, enabling you to generate a model, update directives, or export output in the appropriate format, as needed.