Experiment 5 · about 12 min

Decision tree

0/4 tasks

Every day Sam walks, bikes or takes the bus to school. Sam picks one by following a rule, but has never told anyone what it is. Train a decision tree on the diary: can the tree find the rule?

Sam’s diary

Tap a day to add it to the training data. The tree only learns from the days you pick.

0 days in training

The learned tree

Most questions

Pick a few days from the diary and the tree will grow here.

Test the tree

Let the tree guess 8 of Sam’s days it has never seen.

Tasks

Add at least 6 days to training (waiting)
Find a day the tree gets wrong, ask Sam and teach the tree (waiting)
Get all 8 test days right (waiting)
Set the question limit to 1 and look at the test result (waiting)

What’s going on?

At every step the tree picks the question that splits the days best. The best question leaves each group as alike as possible: all the walking days on one side and all the bus days on the other, for example. Then it does the same inside each group.

Every question in the tree is an if, and every leaf is a result. That is exactly what the “If” block does in block coding; here you don’t write the rule, the model works it out from examples.

Does the tree ask about the temperature? If not, it has worked out on its own that the temperature plays no part in Sam’s choice.

Try this: pick only dry days. The tree never asks about rain, because it can’t learn something it has never seen in the examples. Then see what it says about a rainy day.

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Lab