Variable interaction refers to the multiplication of two variables, which can be numerical variable * numerical variable, or categorical variable * categorical variable.

Combined feature is one of the most important methods in feature engineering. It combines two or more class attributes into one. This is a very useful technique when a combined feature is better than a single feature.

For example, two numerical variables and two categorical variables in the house price data are interacted into combined features respectively

A2 Interact two numerical variables to generate "SubClass_LotFrontage" and interact two categorical variables to generate "MSZoning_LotShape"