How to Sort Bar Chart Items

Hello,
i am trying to understand how to sort the items in a bar chart but i'm having no luck.
I have a report whose items have this structure:
{
Year: "2016"
country: "Austria"
countryOrder: 1
Amount: 1
}
And this is the structure of the report:

    return {
      dataSource: {
        data: getData()
      },
      slice: {
        rows: [
          {
            uniqueName: "country",
          },
        ],
        columns: [
          {
            uniqueName: "[Measures]",
          },
        ],
        measures: [
          {
            uniqueName: "Amount",
            aggregation: "sum",
          },
        ],
        expands: {
          expandAll: true,
        },
        drills: {
          drillAll: true,
        },
      },
      options: {
        viewType: "charts",
        grid: {
          type: "classic",
          showTotals: "off",
          showGrandTotals: "rows",
        },
      },
    };
  }

 
I would like to order the items by "countryOrder" field, i tried with the custom sorting but i think that i cannot sort a field that is not in slice object.
Can you please help me?
Thank you