# Decision Tree Visualization

This page contains a guide the many options for visualizing tree learners.

## Interactive Visualizations

### Tree Visualization

The write_html function allows you to construct an interactive browser visualization of a tree learner:

IAI.write_html("tree.html", lnr)
Optimal Trees Visualization

In a Jupyter notebook, tree learners are automatically visualized in this way. If you are working from a terminal, you can open a browser window with a visualization of any tree learner using show_in_browser.

### Questionnaires

The write_questionnaire function allows you to create an interactive questionnaire from a tree learner.

You can open a browser window with the questionnaire for any tree learner using show_questionnaire.

### Multi-learner Interactive Visualizations

It is possible to combine many learners into a single interactive visualization that will present the user with the ability to change between the trees. We combine the learners as follows:

• a question is a Pair of the form question => responses where question is the string prompt for the question and responses is a vector of possible responses
• each response is also a Pair of the form answer => next where answer is the string answer for this option, and next indicates how to proceed if this response is selected. The possible options for next are:
• another question to continue presenting options
• a tree learner to visualize

The following example prepares a series of questions to choose between a group of learners:

questions = ("Use tree" => [
"with hyperplanes" => lnr_hyper,
"without hyperplanes" => ("and maximum depth" => [
"1" => lnr_nohyper_depth1,
"2" => lnr_nohyper_depth2,
]),
])

We pass this to MultiTreePlot or MultiQuestionnaire to construct the visualization, which can then be saved to file with write_html or opened in the browser with show_in_browser as desired:

IAI.MultiTreePlot(questions)
Optimal Trees Visualization

## Static Images

The write_png function allows you to visualize a tree learner as a PNG image:

IAI.write_png("tree.png", lnr)

Note that this requires you have GraphViz installed and on the system PATH. If you do not, you can use write_dot to export the tree in .dot format and use GraphViz to render it as a PNG image at a later time.

## Miscellaneous

### Missing values

When displaying the tree in the terminal or as an image, if the observations with missing observations goes to the lower child, the split message will say is missing in addition to the split criterion. Otherwise, no explicit message is displayed regarding the missing data direction.

Fitted OptimalTreeClassifier:
1) Split: XS3obtfU < 39.34
2) Split: Fr8w5mB0 ≤ 3 or is missing
3) Predict: 1 (92.66%), [8,101], 109 points, error 8
4) Predict: 0 (100.00%), [43,0], 43 points, error 0
5) Split: zAPikvQB is missing
6) Predict: 1 (91.11%), [8,82], 90 points, error 8
7) Predict: 0 (91.86%), [237,21], 258 points, error 21

In the interactive tree visualization, the child node that receives data with missing values is denoted by a small dot on top of the node.

Optimal Trees Visualization