How to do custom aggregate functions?

[Dom]

I've looked over documentation but was not able to find an example on how to implement custom aggregate function for a data source. Is that possible? Can someone post simple example?

Thanks,
Dominik

[Dom]

Is it possible to get a value of the group on so that I can pass it to a function and use it in the template? Like this:

columns: [
//some other column definitions go here
        { field: "ValueAmount", title: "Modifier Value", format: "{0:N2}", groupFooterTemplate: "#= ValueAmountBalance(/* groupId */) #" },
        { field: "OverrideAmount", title: "Override", format: "{0:N2}", groupFooterTemplate: "#= OverrideAmountBalance(/* groupId */) #" }
      ],

[Alexander Valchev]

Hi Dom,

I have already replied to your question in the support ticket that you submitted on the same subject. For convenience I will paste my reply here, so the other users who follow this thread could read it.

I am afraid that the dataSource does not support custom aggregate functions. By default the groupFooterTemplate contains information about current group aggregates, but not the "group by" field and value. As a workaround I can suggest to retrieve this information through thegroupHeaderTemplate (groupHeaderTemplate is executed before groupFooterTemplate). As an example:

{ field: "category", groupHeaderTemplate: "# getGroupInfo(data) #" },
{ field: "amount", groupFooterTemplate: "#= calculateAggregate(groupByField, groupByValue) #" }

function getGroupInfo(data) {
    groupByField = data.field;
    groupByValue = data.value;
};
//where groupByField and groupByValue are global variables

function calculateAggregate(field, value) {
    return field + " " + value;
}

Alternatively you may consider using the dataSource.view() which contains information about the group field, value and items. The order of view objects matches the order of displayed items(groups) in the grid. 

To avoid any further duplication I would like to ask you to continue our conversation in the support ticket.
Thank you in advance.

Kind regards,
Alexander Valchev
the Telerik team

[Geoff]

Is this still the most up to date answer?

[Alexander Valchev]

Hello Geoff,

The previous answer is still valid.

Regards,
Alexander Valchev
Telerik