# RowGrouping A collection of row selections that have the same value in a column. ``` struct RowGrouping where GroupingKey : Hashable ``` ## Topics ### Creating a Row Grouping [`init(frame: D, columnName: String, timeUnit: Calendar.Component)`](/documentation/TabularData/RowGrouping/init(frame:columnName:timeUnit:)) Creates a row grouping from a column with date or time elements. [`init(groups: [(GroupingKey?, D)], groupKeysColumnName: String)`](/documentation/TabularData/RowGrouping/init(groups:groupKeysColumnName:)) Creates a row grouping from a list of groups. ### Inspecting a Row Grouping [`var count: Int`](/documentation/TabularData/RowGrouping/count) The number of groups in the row grouping. [`subscript(Int) -> (key: GroupingKey?, group: DataFrame.Slice)`](/documentation/TabularData/RowGrouping/subscript(_:)-5z2eg) Retrieves a group at an index. ### Transforming a Row Grouping [`func mapGroups((DataFrame.Slice) throws -> DataFrame) rethrows -> RowGrouping`](/documentation/TabularData/RowGrouping/mapGroups(_:)) Generates a row grouping that applies a transformation closure to each group in the original. ### Splitting a Row Grouping [`func randomSplit(by: Double, seed: Int?) -> (RowGrouping, RowGrouping)`](/documentation/TabularData/RowGrouping/randomSplit(by:seed:)) Generates two row groupings by randomly splitting the original with a proportion and a seed number. ### Aggregating a Row Grouping [`func counts(order: Order?) -> DataFrame`](/documentation/TabularData/RowGrouping/counts(order:)) Generates a data frame with two columns, one that has a row for each group key and another for the number of rows in the group. [`func aggregated(on: [String], naming: (String) -> String, transform: (DiscontiguousColumnSlice) throws -> Result?) rethrows -> DataFrame`](/documentation/TabularData/RowGrouping/aggregated(on:naming:transform:)) Generates a data frame by aggregating each group’s contents for each column you list by name. ### Flattening a Row Grouping [`func ungrouped() -> DataFrame`](/documentation/TabularData/RowGrouping/ungrouped()) Generates a data frame that contains all the rows from each group in the row grouping. ### Summarizing a Row Grouping [`func summary() -> any GroupSummaries`](/documentation/TabularData/RowGrouping/summary()) Generates a group summaries instance for the columns of the row grouping. [`func summary(of: [String]) -> any GroupSummaries`](/documentation/TabularData/RowGrouping/summary(of:)) Generates a group summaries instance for the columns you select by name. [`protocol GroupSummaries`](/documentation/TabularData/GroupSummaries) A collection of group summaries. ### Describing a Row Grouping [`var description: String`](/documentation/TabularData/RowGrouping/description) A text representation of the row grouping. ### Invoking Protocol Methods ### Subscripts [`subscript(Any?...) -> DataFrame.Slice?`](/documentation/TabularData/RowGrouping/subscript(_:)-2xxs8) Retrieves a group slice by key. ### Default Implementations [Collection Implementations](/documentation/TabularData/RowGrouping/Collection-Implementations) [RandomAccessCollection Implementations](/documentation/TabularData/RowGrouping/RandomAccessCollection-Implementations) [RowGroupingProtocol Implementations](/documentation/TabularData/RowGrouping/RowGroupingProtocol-Implementations) ## Relationships ### Conforms To [`Collection`](/documentation/Swift/Collection) [`Copyable`](/documentation/Swift/Copyable) [`RowGroupingProtocol`](/documentation/TabularData/RowGroupingProtocol) [`Escapable`](/documentation/Swift/Escapable) [`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible) [`RandomAccessCollection`](/documentation/Swift/RandomAccessCollection) [`Sequence`](/documentation/Swift/Sequence) [`BidirectionalCollection`](/documentation/Swift/BidirectionalCollection) --- 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)