Last night I was hacking out a lambda to generate an Excel column label.

I got to this – it looks a bit messy to me – can anyone come up with an improvement?

Essentially the use case is to generate these strings, in order: A,B,C…Z,AA,AB,AC…AZ,BA,BB,BC…BZ,…,ZA..ZZ, AAA, AAB, AAC…ad infinitum.



 var letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

 var i = new List(){0};

 Func<String> getNextColumn = () =>

 {

   var sb = new StringBuilder();

   var addOne = false;

   var incIndex = -1;

   for (var j = 0; j < i.Count; j++)

   {

    var n = i[j];

    sb.Append(letters[n]);

    if (j == i.Count - 1)

    {

     n = n + 1;

    }

    if (n > letters.Length - 1)

    {

     n = 0;

     if (j == 0)

     {

      addOne = true;

     }

     else if (letters[i[j - 1]] == 'Z')

     {

      addOne = true;

     }

     else

     {

      incIndex = j - 1;

     }

    }

    i[j] = n;

   }

   if (addOne) { i.Add(0); }

   if (incIndex >= 0) { i[incIndex] += 1; }

   return sb.ToString();

 };



This lambda is defined within a function that generates cells (rows are easy, cos they are just sequential numbers). The function itself is then creating a sheet and calling off ‘getNextColumn’ when it needs to.