How to convert Excel sheet column names into numbers? [duplicate]

Answer 1

I had to deal with this a few months ago. The inverse - column index to column name - is fun, too, and becomes really messy if you try to solve it with a zero based index not recognizing that this complicates things. It could be so simple if it would be a normal polyadic numeral system ...

Here is a simplified version of my solution as a extension method without error handling and all that stuff.

public static Int32 ToOneBasedIndex(this String name)
{
    return name.ToUpper().
       Aggregate(0, (column, letter) => 26 * column + letter - 'A' + 1);
}