Useful Code Snippet for finding columns in Excel

Artikel
03/20/2009

Hi all,

I have been working on a project for a while now and needed a quick converter between an integer index and the column of an Excel spreadsheet, I couldn’t find a general algorithm, so had to write one…

At first I thought it was a simple base 26 (26 letters in the alphabet) system, but then realized that with the first column being indexed as 0 or 1 there would be an inconsistency when you get to the 26th column (where it should read “AA”, or “10” in a base 26 system), “A” is both representing the values 0 and 1.

I worked for a while on an algorithm to calculate the correct value and have come up with the following static class to do it:

Converting between integer index and Column string:

 using System;

using System.Diagnostics;

/// <summary>

/// Converter from numberical index of column to the identifier in excel

/// </summary>

public static class Column

   /// <summary>

   /// Array of alphabet

   /// </summary>

   private static string[] alphabet = { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" };

   /// <summary>

   /// Converts from numberical index of column to the identifier in excel

   /// </summary>

   /// <param name="index">The index of the column</param>

   /// <returns>The corrisponding letter string of that column</returns>

   public static string Index(int index)

      string value = string.Empty;

      int Base = alphabet.Length;

      int currentPower = 0;

      if (index >= 0)

do

            if (Math.Pow(Base, currentPower) < int.MaxValue)

               value = alphabet[((index - RecursivePower(Base, currentPower)) / (int)Math.Pow(Base, currentPower)) % Base] + value;

               currentPower++;

            else

               Trace.WriteLine("That index is too high for the value of MaxInt on this system, so can not continue");

               return string.Empty;

         while (RecursivePower(Base, currentPower) <= index);

      return value;

   /// <summary>

   /// Do a recursive summing of powers from starting power to 1

   /// </summary>

   /// <param name="theBase"></param>

   /// <param name="startingPower"></param>

   /// <returns>The sum of the powers of theBase to 1 (0 if power starts > 1)</returns>

   private static int RecursivePower(int theBase, int startingPower)

      int value = 0;

      for (int i = startingPower; i > 0; i--)

         value += (int) Math.Pow(theBase, i);

      return value;

I hope that helps anyone trying to do this… again it can be ported into VB if you want to script it, and remember where I used alphabet as an array you could always use Chr(index calculation here + 65) which I believe indexes the “A” character when 0 is added to it.

Comments

Anonymous
March 20, 2009
Are you trolling for interview candidates? ;-) string ColumnName(unsigned n) { vector<char> digits; while (n > 25) { digits.push_back(n % 26 + 'A'); n = n / 26 - 1; } digits.push_back(n + 'A'); return string(digits.rbegin(), digits.rend()); }
Anonymous
March 22, 2009
C++ guy: no, to be honest I tried looking for an algorithm in c# for a while without finding one, so tried figuring it out myself. I have just ported your code into C# and have: public string ColumnName(uint n) { string digits = string.Empty; while (n > 25) { digits = ((char)(n % 26 + (int)'A')) + digits; n = n / 26 - 1; } digits = ((char)(n + (int)'A')) + digits; return digits; } which works nicely, though I'm not too happy about casting from chars to ints in a higher level language, but thanks still. I'm just surprised that I couldn't find this code when I was looking before :

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Useful Code Snippet for finding columns in Excel

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