# OneHotEncoder.Transformer A transformer that encodes a category as an array of integers. ``` struct Transformer ``` ## Topics ### Creating a transformer [`init(categories: Set)`](/documentation/CreateMLComponents/OneHotEncoder/Transformer/init(categories:)) Creates a one-hot encoder. ### Getting the categories [`var categories: Set`](/documentation/CreateMLComponents/OneHotEncoder/Transformer/categories) Unique values to encode [`func category(at: Int) -> Category?`](/documentation/CreateMLComponents/OneHotEncoder/Transformer/category(at:)) Retrieves the category at the one-hot encoding index. ### Performing the transformation [`func applied(S, eventHandler: EventHandler?) throws -> [[Int]]`](/documentation/CreateMLComponents/OneHotEncoder/Transformer/applied(_:eventHandler:)) Performs a one-hot encoding on a sequence of inputs. [`func applied(to: Category?, eventHandler: EventHandler?) throws -> [Int]`](/documentation/CreateMLComponents/OneHotEncoder/Transformer/applied(to:eventHandler:)) Performs a one-hot encoding on a single input. ### Default Implementations [Decodable Implementations](/documentation/CreateMLComponents/OneHotEncoder/Transformer/Decodable-Implementations) [Encodable Implementations](/documentation/CreateMLComponents/OneHotEncoder/Transformer/Encodable-Implementations) ## Relationships ### Conforms To [`Escapable`](/documentation/Swift/Escapable) [`Decodable`](/documentation/Swift/Decodable) [`Transformer`](/documentation/CreateMLComponents/Transformer) [`Sendable`](/documentation/Swift/Sendable) [`Copyable`](/documentation/Swift/Copyable) [`Encodable`](/documentation/Swift/Encodable) [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`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)