title: Pyspark: save transformers
body: <p>I am using some transformers of Pyspark such as StringIndexer, StandardScaler and more. I first apply those to the training set and then later on I want to use the same transformation objects (same parameters of StringIndexerModel, StandardScalerModel) in order to apply them on the test set. Therefore, I am looking for a way to save those transformation functions as a file. However, I cannot find any related method but only with ml functions such as LogisticRegression. Do you know any possible way to do that? Thanks.</p>