CustomAggegrate function has already support this scenario. For example if you wish to calculate the sum[ValueX] / sum[Value] on the column Date. Here is the snippet:

protected void wgTest_CustomAggregate(object sender, ISNet.WebUI.WebGrid.CustomAggregateArgs e)
{
    if (e.Column.DataMember == "Date")
    {
        WebGridRowCollection rows = e.Rows;
        Double sumVal = 0;
        Double sumValX = 0;
        for (int i = 0; i < rows.Count; i++)
        {
            WebGridCell cellVal = rows[i].Cells.GetNamedItem("Value");
            sumVal += (Double)cellVal.Value;

            WebGridCell cellValX = rows[i].Cells.GetNamedItem("ValueX");
            sumValX += (Double)cellValX.Value;
        }

        e.AggregateResult = ((Double)(sumValX / sumVal)).ToString("#.#0");
    }
}

In this example both the Value and ValueX column has a Double datatype.

You could read the CustomAggegrate walkthrough in or WebGrid documentation under the article "Walkthrough: Using Custom Aggregate function in WebGrid"

Thanks a lot, If webgrid in SelfReferencing mode and ColumnFooterAggregateMode="CalculateAllData", how to use CustomAggregate API calculate all data? this example only  calculate the level 1 rows. not all data.

Best Regards

You could modify the snippet so instead of iterating e.Rows you will iterate the WebGrid datasource or you will need to requery the data if the WebGrid do not cache the data.

Here is the updated snippet that will iterate the WebGrid datasource, in my scenario the DataSource is a DataTable:

protected void wgTest_CustomAggregate(object sender, ISNet.WebUI.WebGrid.CustomAggregateArgs e)
{
    if (e.Column.DataMember == "Date")
    {
        DataTable dtSource = (DataTable)wgTest.GetCachedDataSource();
        Double sumVal = 0;
        Double sumValX = 0;
        for (int i = 0; i < dtSource.Rows.Count; i++)
        {
            sumVal += (Double)dtSource.Rows[i]["Value"];

            sumValX += (Double)dtSource.Rows[i]["ValueX"];
        }

        e.AggregateResult = sumValX + " / " + sumVal + " : " + ((Double)(sumValX / sumVal)).ToString("#.#0");
    }
}

I try to using the snippet code, but GetCachedDataSource() function always return null, (AllowAutoDataCaching=True, AlwaysUseCachedDataOnFirstLoad=False). How can i do?

Best Regards

Thank you, I make a mistake, so GetCachedDataSource() return is null, now it can work, thanks again

Best Regards