//Create a new workbook
var workbook = new GrapeCity.Documents.Excel.Workbook();           
//Load sample data from excel file
workbook.Open("SampleData.xlsx");
//Enable dynamic array formula
workbook.AllowDynamicArray = true;

//Fetch worksheet
var worksheet = workbook.Worksheets[0];
//Fetch the original formula which needs to be parsed.
var originalFormula = worksheet.Range["H3"].Formula.Substring(1);

//Method to parse a formula and print the syntax tree
public static void ParseAndPrint(IWorksheet worksheet, string formula)
{
   // Get syntax tree
   var syntaxTree = FormulaSyntaxTree.Parse(formula);

   // Flatten nodes
   var displayItems = new List<(string TypeName, int IndentLevel, string Content)>();

   void flatten(SyntaxNode node, int level)
   {
      displayItems.Add((node.GetType().Name, level, node.ToString()));
      foreach (var child in node.Children)
      {
         flatten(child, level + 1);
      }
   }

   flatten(syntaxTree.Root, 0);

   // Output          
   worksheet.ShowRowOutline = false;
   worksheet.OutlineColumn.ColumnIndex = 1;

   // Header
   worksheet.Range["A1"].Value = "Formula";
   worksheet.Range["A3"].Value = "Syntax node";
   worksheet.Range["B3"].Value = "Part";

   // Values
   worksheet.Range["B1"].Value = "'=" + formula;
   for (var i = 0; i < displayItems.Count; i++)
   {
      var item = displayItems[i];
      var text = "'" + item.TypeName;

      worksheet.Range[i + 4, 0].Value = text;
      worksheet.Range[i + 4, 0].IndentLevel = item.IndentLevel;
      worksheet.Range[i + 4, 1].Value = "'" + item.Content;
   }

   //Apply styling
   worksheet.Range["A1:B3"].Interior.Color = System.Drawing.Color.FromArgb(68, 114, 196);
   worksheet.Range["A1:B3"].Font.Color = System.Drawing.Color.White;
   worksheet.Range["A1:B3"].Borders.Color = System.Drawing.Color.FromArgb(91, 155, 213);
   worksheet.Range["A1:B3"].Borders.LineStyle = BorderLineStyle.Thin;
   worksheet.Range["A1,A3,B3"].Font.Size = 14;
   worksheet.Range["A1,A3,B3"].Font.Bold = true;
   worksheet.Range["A:C"].EntireColumn.AutoFit();           
}

//Method to parse and modify the formula
public static void ModifyFormula(IWorksheet worksheet, string originalFormula)
{
    //Apply UNIQUE formula to get unique sales representatives list
    worksheet.Range["F1"].Value = "Unique Rep";
    worksheet.Range["F2"].Formula = "=UNIQUE(A2:A19)";
    var uniqueRep = worksheet.Range["F2#"];
    // Apply Styling
    worksheet.Range["F:F"].EntireColumn.AutoFit();
    worksheet.Range["F1"].Interior.Color = System.Drawing.Color.FromArgb(68, 114, 196);
    worksheet.Range["F1"].Font.Color = System.Drawing.Color.White;
    worksheet.Range["F2#"].Borders.Color = System.Drawing.Color.FromArgb(91, 155, 213);
    worksheet.Range["F2#"].Borders.LineStyle = BorderLineStyle.Thin;

    //Get syntax tree
    var syntaxTree = FormulaSyntaxTree.Parse(originalFormula);

    //Find
    var findText = new TextNode("Fritz");

    //Replacement
    var replaceText = new TextNode("");

    //Loop through names list to modify the formula for each sales representative
    for (int r = 0, resultRow = 3; r < uniqueRep.Cells.Count; r++, resultRow = resultRow + 4)
    {
       //Get name to be replaced in the formula
       var cval = uniqueRep.Cells[r].Value.ToString();

       if (findText.Value != cval)
       {
          //Assign name to be replaced to Replace TextNode
          replaceText.Value = cval;

          //Invoke the recursive method to perform find and replace operation
          replaceNode(syntaxTree.Root, findText, replaceText);

          //Assign the modified formula to a cell in the worksheet
          var resultRange = "H" + resultRow.ToString();
          worksheet.Range[resultRange].Formula = "=" + syntaxTree.ToString();
          worksheet.Range[resultRange + "#"].Borders.Color = System.Drawing.Color.FromArgb(91, 155, 213);
          worksheet.Range[resultRange + "#"].Borders.LineStyle = BorderLineStyle.Thin;

          //Update the value of Find node to perform find and replace operation for next sales representative name
          findText = replaceText;
       }
    }

    //Find and replace
    void replaceNode(SyntaxNode lookIn, SyntaxNode find, SyntaxNode replacement)
    {
       var children = lookIn.Children;

       for (var i = 0; i < children.Count; i++)
       {
          var child = children[i];
          if (child.Equals(find))
          {
             children[i] = replacement;
          }
          else
          {
             replaceNode(child, find, replacement);
          }
       }
    }
 }

//Save modified Excel file
workbook.Save("ModifiedFormula.xlsx", SaveFileFormat.Xlsx);