4. Of Bikes and Men

So far, the problems we have tackled have involved classifying items between a limited set of possible categories. While classification has applications in many practical situations, an arguably more common problem is to predict a number. Consider, for instance, the following task: Given the characteristics of a used car (age, miles, engine size, and so forth), how would you go about predicting how much it is going to sell for? This problem doesn't really fit the pattern of classification. What we need here is a model that differs from classification models in at least two aspects: