Fastest way to interface between live (unsaved) Excel data and C# objects

I’ll take this as a challenge, and will bet the fastest way to shuffle your data between Excel and C# is to use Excel-DNA – http://excel-dna.net.
(Disclaimer: I develop Excel-DNA. But it’s still true…)

Because it uses the native .xll interface it skips all the COM integration overhead that you’d have with VSTO or another COM-based add-in approach. With Excel-DNA you could make a macro that is hooked up to a menu or ribbon button which reads a range, processes it, and writes it back to a range in Excel. All using the native Excel interface from C# – not a COM object in sight.

I’ve made a small test function that takes the current selection into an array, squares every number in the array, and writes the result into Sheet 2 starting from cell A1. You just need to add the (free) Excel-DNA runtime which you can download from http://excel-dna.net.

I read into C#, process and write back to Excel a million-cell range in under a second. Is this fast enough for you?

My function looks like this:

using ExcelDna.Integration;
public static class RangeTools {

[ExcelCommand(MenuName="Range Tools", MenuText="Square Selection")]
public static void SquareRange()
{
    object[,] result;
    
    // Get a reference to the current selection
    ExcelReference selection = (ExcelReference)XlCall.Excel(XlCall.xlfSelection);
    // Get the value of the selection
    object selectionContent = selection.GetValue();
    if (selectionContent is object[,])
    {
        object[,] values = (object[,])selectionContent;
        int rows = values.GetLength(0);
        int cols = values.GetLength(1);
        result = new object[rows,cols];
        
        // Process the values
        for (int i = 0; i < rows; i++)
        {
            for (int j = 0; j < cols; j++)
            {
                if (values[i,j] is double)
                {
                    double val = (double)values[i,j];
                    result[i,j] = val * val;
                }
                else
                {
                    result[i,j] = values[i,j];
                }
            }
        }
    }
    else if (selectionContent is double)
    {
        double value = (double)selectionContent;
        result = new object[,] {{value * value}}; 
    }
    else
    {
        result = new object[,] {{"Selection was not a range or a number, but " + selectionContent.ToString()}};
    }
    
    // Now create the target reference that will refer to Sheet 2, getting a reference that contains the SheetId first
    ExcelReference sheet2 = (ExcelReference)XlCall.Excel(XlCall.xlSheetId, "Sheet2"); // Throws exception if no Sheet2 exists
    // ... then creating the reference with the right size as new ExcelReference(RowFirst, RowLast, ColFirst, ColLast, SheetId)
    int resultRows = result.GetLength(0);
    int resultCols = result.GetLength(1);
    ExcelReference target = new ExcelReference(0, resultRows-1, 0, resultCols-1, sheet2.SheetId);
    // Finally setting the result into the target range.
    target.SetValue(result);
}
}