Translate an index into an Excel Column Name

Question

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

The problem is tricker than it sounds because the columns don't wrap over like normal digits would. Even the Microsoft Support Example doesn't scale beyond ZZZ.

Disclaimer: This is some code I had done a while back, and it came across my desktop again today. I thought it was worthy of posting here as a pre-answered question.

Answer 1

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 2

It's for this very reason that I avoid column names in programmed interface to Excel. Using column numbers works very well in Cell(r,c) references and R1C1 addressing.

EDIT: The Range function also takes cell references, as in Range(Cell(r1,c1),Cell(r2,c2)). Also, you can use the Address function to get the A1-style address of a cell or range.

EDIT2: Here's a VBA function that uses the Address() function to retrieve the column name:

Function colname(colindex)
    x = Cells(1, colindex).Address(False, False) ' get the range name (e.g. AB1)
    colname = Mid(x, 1, Len(x) - 1)              ' return all but last character
End Function

Answer 3

This has already been asked on stackoverflow, see my answer here.

Answer 4

Here's Joel's awesome code modified to work with zero-based column indexes and without the char array.

 Public Shared Function GetExcelColumn(ByVal index As Integer) As String

        Dim quotient As Integer = index \ 26 ''//Truncate 
        If quotient > 0 Then
            Return GetExcelColumn(quotient - 1) & Chr((index Mod 26) + 65).ToString

        Else
            Return Chr(index + 65).ToString

        End If

    End Function

Many thanks to Joel for getting me on the right track!

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

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;
    }