This was asked by someone but the answer like the following does not serve my purpose...
var dg=$('#dg');
var selected = dg.datagrid('getRowIndex',dg.datagrid('getSelected')));
var selections= dg.datagrid('getRowIndex',dg.datagrid('getSelections')));
var ids = [];
$.each(Selections, function(i, e){
var index = dg.datagrid('getRowIndex', e);
if(ids.contains(e.id)){
console.info('exists index -->>' + index)
}else{
ids.push(e.id);
}
});