# subscript(_:) Retrieves or adds an untyped column with the specified name. ``` subscript(columnName: String) -> MLUntypedColumn { get set } ``` ## Parameters `columnName` The name of the column to extract from or add to the datatable. ## Return Value A new [`MLUntypedColumn`](/documentation/CreateML/MLUntypedColumn) with the specified name, if it exists; otherwise an invalid column. ## Overview Use this subscript to retrieve an [`MLUntypedColumn`](/documentation/CreateML/MLUntypedColumn) or add a new one to the data table. > Important: The number of elements in the column must equal the number > of rows in the data table. Otherwise, the data table will be > invalidated. -3wjk-1@2x.png) For example, to extract, convert, and add a column as shown above, begin by creating a data table. ```swift let data: [String: MLDataValueConvertible] = [ "Planet": ["Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune"], "Distance (AU)": [0.39, 0.72, 1.00, 1.52, 5.20, 9.54, 19.22, 30.06] ] var table = try MLDataTable(dictionary: data) ``` After creating the table, extract a column. ```swift let distanceInAU = table["Distance (AU)"] ``` > Note: Without a type annotation, the compiler uses this version of > `subscript(_:)` instead of the equivalent > ``doc://com.apple.createml/documentation/CreateML/MLDataTable/subscript(_:)-5tl9r`` from ``doc://com.apple.createml/documentation/CreateML/MLDataColumn``. Use the untyped column’s multiplication operator to create a new column of data. ```swift // Create a new column of Doubles by multiplying all the the values in // `distanceInAU` by 149,597,870.7 (the number of km in an astronomical unit) let distanceInKm = (distanceInAU * 149_597_870.700) ``` Finally, use the `subscript(_:)` to add the new column to a table with a different name. ```swift table["Distance (km)"] = distanceInKm ``` > Important: To replace a column, use > ``doc://com.apple.createml/documentation/CreateML/MLDataTable/removeColumn(named:)`` before adding its replacement. > Adding a column with the same name as one already in the data table may > invalidate the data table. --- 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)