# aggregated(on:naming:transform:) Generates a data frame by aggregating each group’s contents for each column you select by name. ``` func aggregated(on columnNames: [String], naming: (String) -> String, transform: (DiscontiguousColumnSlice) throws -> Result?) rethrows -> DataFrame ``` ## Parameters `columnNames` A comma-separated, or variadic, list of column names. `naming` A closure that converts a column name to another name. `transform` A closure that aggregates a group’s elements in a specific column. ## Discussion The data frame contains two columns that: - Identify each group - Store the results of your aggregation transform closure --- 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)