병합된 셀의 합계 계산

var columns = [
  ...생략...
  {
    name: "Age",
    fieldName: "Age",
    width: 50,
    mergeRule: "value",
    header: {
      text: "나이",
      styleName: "orange-column"
    },
    numberFormat: "#,##0",
    footer: {
      valueCallback: function(grid, column, footerIndex, columnFooter, value){
        var sum = 0;
        var i = 0;
        var iCnt = grid.getItemCount();
    
        while(i < iCnt) {
            var items = grid.getMergedItems(i, column.name);
            sum += grid.getValue(items[0], column.name);
            i += items.length;
        }
    
        return sum;
      },
      numberFormat: "#,##0",
      styleName: "center-column"
    }
  },
  ...생략...
];