	bool HasColumn(const std::string& column, size_t& index) CXX11_OVERRIDE
	{
		for (size_t i = 0; i < colnames.size(); ++i)
		{
			if (colnames[i] == column)
			{
				index = i;
				return true;
			}
		}
		return false;
	}
	bool HasColumn(const std::string& column, size_t& index) CXX11_OVERRIDE
	{
		for (size_t i = 0; i < colnames.size(); ++i)
		{
			if (colnames[i] == column)
			{
				index = i;
				return true;
			}
		}
		return false;
	}