tended to multi-level classification as well.  

**Regression** is used when the target `\(y\)` outcome variable is continuous. Regression models the conditional expectation (conditional mean) of the outcome variable given the covariates: `\(E(y | x)\)`.  

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# Data preprocessing

A longstanding first step is to split a dataset into **"training"** and **"test"** subsets. A training sample usually consists of a majority of the original dataset so that an algorithm can learn the model. The remaining portio