Translate a column index into an Excel Column Name

Question

Given a columns\' index, how can you get an Excel column name?

The problem is trickier than it sounds because it\'s not just base-26. The columns

Answer 1

public static String translateColumnIndexToName(int index) {
        //assert (index >= 0);

        int quotient = (index)/ 26;

        if (quotient > 0) {
            return translateColumnIndexToName(quotient-1) + (char) ((index % 26) + 65);
        } else {
            return "" + (char) ((index % 26) + 65);
        }


    }

and the test:

for (int i = 0; i < 100; i++) {
            System.out.println(i + ": " + translateColumnIndexToName(i));
}

here is the output:

0: A
1: B
2: C
3: D
4: E
5: F
6: G
7: H
8: I
9: J
10: K
11: L
12: M
13: N
14: O
15: P
16: Q
17: R
18: S
19: T
20: U
21: V
22: W
23: X
24: Y
25: Z
26: AA
27: AB
28: AC

I needed 0 based for POI

and translation from index to names:

public static int translateComunNameToIndex0(String columnName) {
        if (columnName == null) {
            return -1;
        }
        columnName = columnName.toUpperCase().trim();

        int colNo = -1;

        switch (columnName.length()) {
            case 1:
                colNo = (int) columnName.charAt(0) - 64;
                break;
            case 2:
                colNo = ((int) columnName.charAt(0) - 64) * 26 + ((int) columnName.charAt(1) - 64);
                break;
            default:
                //illegal argument exception
                throw new IllegalArgumentException(columnName);
        }

        return colNo;
    }

Answer 2

I enjoy writing recursive functions, but I don't think it's necessary here. This is my solution in VB. It works up to column ZZ. If someone can tell me if it works for AAA to ZZZ that would be nice to know.

Public Function TranslateColumnIndexToName(index As Integer) As String
'
Dim remainder As Integer
Dim remainder2 As Integer
Dim quotient As Integer
Dim quotient2 As Integer
'
quotient2 = ((index) / (26 * 26)) - 2
remainder2 = (index Mod (26 * 26)) - 1
quotient = ((remainder2) / 26) - 2
remainder = (index Mod 26) - 1
'
If quotient2 > 0 Then
    TranslateColumnIndexToName = ChrW(quotient2 + 65) & ChrW(quotient + 65) & ChrW(remainder + 65)
ElseIf quotient > 0 Then
    TranslateColumnIndexToName = ChrW(quotient + 65) & ChrW(remainder + 65)
Else
    TranslateColumnIndexToName = ChrW(remainder + 65)
End If 

End Function

Answer 3

The answer I came up with is to get a little recursive. This code is in VB.Net:

Function ColumnName(ByVal index As Integer) As String
        Static chars() As Char = {"A"c, "B"c, "C"c, "D"c, "E"c, "F"c, "G"c, "H"c, "I"c, "J"c, "K"c, "L"c, "M"c, "N"c, "O"c, "P"c, "Q"c, "R"c, "S"c, "T"c, "U"c, "V"c, "W"c, "X"c, "Y"c, "Z"c}

        index -= 1 ''//adjust so it matches 0-indexed array rather than 1-indexed column

        Dim quotient As Integer = index \ 26 ''//normal / operator rounds. \ does integer division, which truncates
        If quotient > 0 Then
               ColumnName = ColumnName(quotient) & chars(index Mod 26)
        Else
               ColumnName = chars(index Mod 26)
        End If
End Function

And in C#:

string ColumnName(int index)
{
    index -= 1; //adjust so it matches 0-indexed array rather than 1-indexed column

    int quotient = index / 26;
    if (quotient > 0)
        return ColumnName(quotient) + chars[index % 26].ToString();
    else
        return chars[index % 26].ToString();
}
private char[] chars = new char[] {'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'};

The only downside it that it uses 1-indexed columns rather than 0-indexed.

Answer 4

Here is my answer in C#, for translating both ways between column index and column name.

/// <summary>
/// Gets the name of a column given the index, as it would appear in Excel.
/// </summary>
/// <param name="columnIndex">The zero-based column index number.</param>
/// <returns>The name of the column.</returns>
/// <example>Column 0 = A, 26 = AA.</example>
public static string GetColumnName(int columnIndex)
{
    if (columnIndex < 0) throw new ArgumentOutOfRangeException("columnIndex", "Column index cannot be negative.");

    var dividend = columnIndex + 1;
    var columnName = string.Empty;

    while (dividend > 0)
    {
        var modulo = (dividend - 1) % 26;
        columnName = Convert.ToChar(65 + modulo) + columnName;
        dividend = (dividend - modulo) / 26;
    }

    return columnName;
}

/// <summary>
/// Gets the zero-based column index given a column name.
/// </summary>
/// <param name="columnName">The column name.</param>
/// <returns>The index of the column.</returns>
public static int GetColumnIndex(string columnName)
{
    var index = 0;
    var total = 0;
    for (var i = columnName.Length - 1; i >= 0; i--)
        total += (columnName.ToUpperInvariant()[i] - 64) * (int)Math.Pow(26, index++);

    return total - 1;
}

Answer 5

# Python 2.x, no recursive function calls

def colname_from_colx(colx):
    assert colx >= 0
    colname = ''
    r = colx
    while 1:
        r, d = divmod(r, 26)
        colname = chr(d + ord('A')) + colname
        if not r:
            return colname
        r -= 1

Answer 6

Here is my solution in C#

// test
void Main()
{

    for( var i = 0; i< 1000; i++ )
    {   var byte_array = code( i );
        Console.WriteLine("{0} | {1} | {2}", i, byte_array, offset(byte_array));
    }
}

// Converts an offset to AAA code
public string code( int offset )
{
    List<byte> byte_array = new List<byte>();
    while( offset >= 0 )
    {
        byte_array.Add( Convert.ToByte(65 + offset % 26) );
        offset = offset / 26 - 1;
    }
    return ASCIIEncoding.ASCII.GetString( byte_array.ToArray().Reverse().ToArray());
}

// Converts AAA code to an offset
public int offset( string code)
{
    var offset = 0;
    var byte_array = Encoding.ASCII.GetBytes( code ).Reverse().ToArray();
    for( var i = 0; i < byte_array.Length; i++ )
    {
        offset += (byte_array[i] - 65 + 1) * Convert.ToInt32(Math.Pow(26.0, Convert.ToDouble(i)));
    }
    return offset - 1;
}