Grouping

Rows grouped by one or more columns, with a group band to drag captions onto, collapsible group rows and subtotals in their headers and footers.

Install and enable

dotnet add package ArionUI.Grouping --prerelease

Grouping is switched on per view with EnableGrouping(). Columns offer themselves with .WithGrouping(), which is part of the open engine and does nothing until the call is made.

var view = new GridView<Order>(
    [
        Column.Text<Order>("Region", o => o.Region).WithKey("region").WithGrouping(),
        Column.Text<Order>("Customer", o => o.Customer).WithKey("customer").WithGrouping(),
        TypedColumn.Date<Order>("Booked", o => o.Booked).WithKey("booked")
                   .WithGrouping(o => o.Booked.Year, year => $"{year}"),   // by year
        TypedColumn.Number<Order>("Amount", o => (double)o.Amount, format: "N2").WithKey("amount")
                   .Summary(AggregateFn.Sum, o => o.Amount),
    ],
    new ListItemsSource<Order>(orders))
    .AsDataGrid()          // includes the group band and group subtotals
    .EnableGrouping();     // the Pro call: without it nothing groups

WithGrouping(key, label) takes an optional key and label. Without them the column's sort key groups; with them a column can group by something coarser than it shows — a year for a date, a range for an amount.

What the user does

• Drag a column caption into the group band above the header to group by it; drag more for further levels, drag the chips to change the order of the levels, and remove one with the mark at its right end.
• Click the chevron of a group row, or press Space on it, to fold it. The group headers of the rows in view stay pinned at the top while scrolling.
• F6 reaches the group band from the keyboard.

From code

int region = view.ColumnIdOfKey("region");
int customer = view.ColumnIdOfKey("customer");

view.GroupByColumn(region);                 // first level
view.GroupByColumn(customer);               // second level
view.MoveGroup(customer, 0);                // customer becomes the outer level
view.RemoveGroup(region);
bool grouped = view.HasGrouping;
view.ClearGrouping();

GroupedColumns lists the grouped element ids in order; ToggleFirstGroup() folds or unfolds the first group.

Subtotals and options

A column's .Summary(…) serves the grand-total footer and the group rollup with the same arithmetic, so the two cannot disagree. Group aggregates that do not belong to a column go into the view's groupAggregates parameter (see Views).

view.WithGroupPanel(height: 34)                         // the band to drop captions on
    .WithGroupSummaries(header: true, footer: false)    // subtotals in the group header only
    .WithGroupColumnWidth(24);                          // indent per level
grid.CanUserGroupColumns = false;                       // grouping by code only

AsDataGrid() already switches on the group band and subtotals in group headers and footers; each part takes space only once a column is groupable or declares a summary. The group band's hint text is German by default: GroupingUiText.English(), see Localisation.

PDF and print show every group expanded, headers and all; XLSX keeps the groups as an Excel outline; CSV contains the data rows only. A saved layout carries the grouping.