# PreprocessingEstimator An estimator that composes a preprocessing transformer and an estimator. ``` struct PreprocessingEstimator where Preprocessor : Transformer, Estimator : Estimator, Preprocessor.Output == Estimator.Transformer.Input ``` ## Topics ### Creating an estimator [`init(Preprocessor, Estimator)`](/documentation/CreateMLComponents/PreprocessingEstimator/init(_:_:)) Creates a composed estimator from a preprocessing transformer and an estimator. ### Getting the properties [`var estimator: Estimator`](/documentation/CreateMLComponents/PreprocessingEstimator/estimator) The estimator. [`var preprocessor: Preprocessor`](/documentation/CreateMLComponents/PreprocessingEstimator/preprocessor) The preprocessing transformer. ### Preprocesing and fitting [`func preprocessed(from: S, eventHandler: EventHandler?) async throws -> [Preprocessor.Output]`](/documentation/CreateMLComponents/PreprocessingEstimator/preprocessed(from:eventHandler:)) Preprocesses a sequence of examples. [`func fitted(to: S, eventHandler: EventHandler?) async throws -> PreprocessingEstimator.Transformer`](/documentation/CreateMLComponents/PreprocessingEstimator/fitted(to:eventHandler:)) Fits a composed transformer to a sequence of examples. [`func fitted(toPreprocessed: S, eventHandler: EventHandler?) async throws -> PreprocessingEstimator.Transformer`](/documentation/CreateMLComponents/PreprocessingEstimator/fitted(toPreprocessed:eventHandler:)) Fits a transformer to a sequence of preprocessed features. [`typealias Input`](/documentation/CreateMLComponents/PreprocessingEstimator/Input) The input type. [`typealias Intermediate`](/documentation/CreateMLComponents/PreprocessingEstimator/Intermediate) The intermediate type. [`typealias Output`](/documentation/CreateMLComponents/PreprocessingEstimator/Output) The output type. [`protocol Transformer`](/documentation/CreateMLComponents/Transformer) A transformer that takes an input and produces an output. ## Relationships ### Conforms To [`Estimator`](/documentation/CreateMLComponents/Estimator) [`Sendable`](/documentation/Swift/Sendable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)