using mygrid.groupBy(coloumn)

while using using mygrid.groupBy(coloumn) function i am getting the following javacript error

object doesn’t support this method or property

can u tell me where to use the above funcion(after or before data filling)

The method can be used before or after loading data ( it doesn’t matter - it must work in both cases )
Please be sure that codebase/ext/dhtmlxgrid_group.js included in your HTML page