/// <summary>
/// Transpose transpose the table, i.e. exchange columns and rows
/// this can only work if all columns in the table are of the same type
/// </summary>
/// <returns>null if succeeded, error string otherwise</returns>
public virtual string Transpose()
{
// TODO: do also look at the property columns for transposing
_dataColumns.Transpose();
return(null); // no error message
}
