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DB_Table.aggregate

aggregategroup_by columns error_on_missing_columns on_problems

Group: Calculations
Aliases: group by, summarize

Documentation​

Aggregates the rows in a table using group_by columns. The columns argument specifies which additional aggregations to perform and to return.

Arguments​

  • group_by: Vector of column identifiers to group by. These will be included at the start of the resulting table. If no columns are specified a single row will be returned with the aggregate columns.
  • columns: Vector of Aggregate_Column specifying the aggregated table. Expressions can be used within the aggregate column to perform more complicated calculations.
  • error_on_missing_columns: Specifies if a missing columns in aggregates should result in an error regardless of the on_problems settings. Defaults to False, meaning that problematic aggregate will not be included in the result and the problem reported according to the on_problems setting.
  • on_problems: Specifies how to handle problems if they occur, reporting them as warnings by default.

Examples​

Count all the rows​

       table.aggregate columns=[Aggregate_Column.Count]

Group by the Key column, count the rows​

       table.aggregate ["Key"] [Aggregate_Column.Count]

Errors​

  • If there are no columns in the output table, a No_Output_Columns is raised as an error regardless of the problem behavior, because it is not possible to create a table without any columns.
  • If a given aggregate is not supported by the backend, Unsupported_Database_Operation is reported.
  • If a column index is out of range, a Missing_Input_Columns is reported according to the on_problems setting, unless error_on_missing_columns is set to True, in which case it is raised as an error. Problems resolving group_by columns are reported as dataflow errors regardless of these settings, as a missing grouping will completely change semantics of the query.
  • If a column selector is given as a Text and it does not match any columns in the input table nor is it a valid expression, an Invalid_Aggregate_Column error is raised according to the on_problems settings (unless error_on_missing_columns is set to True in which case it will always be an error). Problems resolving group_by columns are reported as dataflow errors regardless of these settings, as a missing grouping will completely change semantics of the query.
  • If an aggregation fails, an Invalid_Aggregation dataflow error is raised.
  • The following additional problems may be reported according to the on_problems settings:
    • If there are invalid column names in the output table, a Invalid_Column_Names.
    • If there are duplicate column names in the output table, a Duplicate_Output_Column_Names.
    • If grouping on or computing the Mode on a floating point number, a Floating_Point_Equality.
    • If when concatenating values there is an quoted delimited, an Unquoted_Delimiter
    • If there are more than 10 issues with a single column, an Additional_Warnings.