Thanks Peter for prompt answer, sample was helpful, actually I wanted to know how can I aggregate data like group by.

for example, In following data, I would like to total for field "Open"  grouped by dates. Is there any way we can get the data from grid?

e.g 

var data = [
{ "DateString": "1/1/2010", "Open": 1000, "High": 1019.75, "Low": 967.75, "Close": 995 },
{ "DateString": "1/1/2010", "Open": 800, "High": 1019.75, "Low": 967.75, "Close": 995 },
{ "DateString": "1/2/2010", "Open": 995, "High": 1016.75, "Low": 975, "Close": 1004 },
{ "DateString": "1/2/2010", "Open": 925.5, "High": 1000.25, "Low": 912.75, "Close": 999.25 },
{ "DateString": "1/3/2010", "Open": 940.25, "High": 1040.25, "Low": 920.75, "Close": 975.25 },
{ "DateString": "1/3/2010", "Open": 1020.5, "High": 1060.25, "Low": 999.75, "Close": 1050.25 }
];

function createPieChart() {
$("#chart1").igDataChart("destroy");
$('#chart1').igPieChart({
dataSource: data,
width: '300px',
height: '300px',
valueMemberPath: 'Open',
labelMemberPath: 'DateString',
// explodedSlices: '0 1',
radiusFactor: .8,
showTooltip: true,
tooltipTemplate: '<div class="tooltip">${item.DateString}</div><div>Open: ${item.Open}</div>',
legend: { element: 'legend', type: 'item' }
});

}

Thanks