var map = {"Very High" : 1, "High" : 2, "Medium" : 3, "Low" : 4};
function get(k){
return map[k];
}
var oSorter = new sap.ui.model.Sorter("Priority");
oSorter.fnCompare = function(value1, value2) {
var val1Mapped = get(value1);
var val2Mapped = get(value2);
if (val1Mapped < val2Mapped) return -1;
if (val1Mapped == val2Mapped) return 0;
if (val1Mapped > val2Mapped) return 1;
};