In Spark ML, what would be an example of a transformer?

In the context of Spark ML, a transformer is a component that takes a DataFrame as input and produces a new DataFrame as output, where the output is transformed in some way. One-hot encoding is a commonly used transformation technique for handling categorical data. It converts each category of a variable into a separate binary column. For example, if you have a categorical variable like "Color" with options such as "Red," "Blue," and "Green," the one-hot encoder will create three new binary columns. Each column will have a value of 1 if the original category matches that column and 0 otherwise. This transformation is crucial as many machine learning algorithms require numerical input, and one-hot encoding effectively represents categorical data in a numerical format.

In contrast, a model used to train data refers to the learning phase rather than transformation. Visualization methods and functions for checking model performance do not fit the definition of transformers in Spark ML, as they serve different purposes within the data processing and model evaluation pipeline. Thus, the one-hot encoder stands out as a clear example of a transformer in Spark ML.