Convert column index into corresponding column letter

Question

I need to convert a Google Spreadsheet column index into its corresponding letter value, for example, given a spreadsheet:

I need to do this (this function obviously does not exist, it's an example):

getColumnLetterByIndex(4);  // this should return "D"
getColumnLetterByIndex(1);  // this should return "A"
getColumnLetterByIndex(6);  // this should return "F"

Now, I don't recall exactly if the index starts from 0 or from 1, anyway the concept should be clear.

I didn't find anything about this on gas documentation.. am I blind? Any idea?

Thank you

Answer 1

I wrote these a while back for various purposes (will return the double-letter column names for column numbers > 26):

function columnToLetter(column)
{
  var temp, letter = '';
  while (column > 0)
  {
    temp = (column - 1) % 26;
    letter = String.fromCharCode(temp + 65) + letter;
    column = (column - temp - 1) / 26;
  }
  return letter;
}

function letterToColumn(letter)
{
  var column = 0, length = letter.length;
  for (var i = 0; i < length; i++)
  {
    column += (letter.charCodeAt(i) - 64) * Math.pow(26, length - i - 1);
  }
  return column;
}