Sea. Animals in the Air and Sea groups were predicted to be non-mammal, while animals in the Land group were predicted to be mammals. This resulted in two errors: bats and frogs. The Has Fur feature divided animals into two groups. Those with fur were predicted to be mammals, while those without fur were not predicted to be mammals. Three errors were counted: pigs, elephants, and rhinos. As the Travels By feature results in fewer errors, the 1R algorithm will return the following "one rule" based on Travels By:
• If the animal travels by air, it is not a mammal
• If the animal travels by land, it is a mammal
• If the animal travels by sea, it is not a mammal
The algorithm stops here, having found the single most important rule.