property Column.GroupByTotalField as String
Indicates the aggregate formula to be displayed when the column gets grouped by.

TypeDescription
String A String expression that indicates the formula to be displayed on the grouping caption.
By default, the GroupByTotalField property is "count(current,rec,1)", which count recursively leaf items ( implies recursively leaf items ) of the grouping item. At runtime, the computed value of this formula is replaced in the HTML format being specified by the GroupByFormatCell property, for the value keyword. When the control is performing a group-by operation, the Items.CellValue(Item,Items.GroupItem(Item)) property is set on GroupByTotalField property, and the Items.CellValueFormat(Item,Items.GroupItem(Item)) is exHTML + exTotalField (5), where the Item is the handle of the item being added during grouping or the Item parameter of the ViewItemUpdate(exAddGroupItem) event. The GroupByTotalField property determines the formula to be applied to the column when it gets grouped. The GroupByFormatCell property determines the format of the cell to be displayed in the grouping item, when the column gets sorted.

For instance 

The syntax for the GroupByTotalField property property should be: aggregate(list,direction,formula) where:

aggregate must be one of the following: 

list must be one of the following:

direction must be one of the following:

Currently, the following items are excluded by aggregate functions:

In conclusion, aggregate functions counts ONLY items that are:

Shortly, by setting to a different value to any of these properties, makes the item to be ignored by the aggregate functions.

For instance