# map(_:) Creates a new column, potentially with missing values, by applying a given thread-safe transform to every row in the data table. ``` func map(_ lazyTransform: @escaping (MLDataTable.Row) -> T?) -> MLDataColumn where T : MLDataValueConvertible ``` ## Parameters `lazyTransform` A thread-safe row transformation function. The implementation of your transform must accept a row from the data table and return an optional type that conforms to `MLDataValueConvertible` . If the transform returns `nil` for a given row, the corresponding element in the new column will have a missing value. ## Return Value A new `MLDataColumn`. ## Discussion This mapping function is the same as `MLDataTable/map(_:)-92wrj` with the exception that this version’s `lazyTransform` parameter returns an optional (`T?`). Use this version of `map()` to create empty values by returning `nil` from your `lazyTransform`. --- 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)