How to enable partial grouping in jqGrid

Question

I need to group my jqgrid partially.

I have a case if the grouping column has more than one record, I have to group otherwise I need to show it directly.

Example : In the below example groupingId is the group column, need to group the first 2 records but not the third record.

var data = [{
groupingId:001,
invoice:1,
amount:5.00
},{
groupingId:001,
invoice:2,
amount:10.00
},{
groupingId:002,
invoice:3,
amount:8.00
}];


var colNames = ['Invoice','Amount'];

Thanks in advance.