R Machine Learning: Introduction

Notation

• X1,...,Xp denote the features, Y denotes the outcomes, and Y^ denotes the predictions.
• Machine learning prediction tasks can be divided into categorical and continuous outcomes. We refer to these as classification and prediction, respectively.
• Yi = an outcome for observation or index i.
• We use boldface for X_i to distinguish the vector of predictors from the individual predictors Xi,1,...,Xi,784.
• When referring to an arbitrary set of features and outcomes, we drop the index i and use Y and bold X.
• Uppercase is used to refer to variables because we think of predictors as random variables.
• Lowercase is used to denote observed values. For example, X=x.