def materialize(self, virtual_column, inplace=False):
        '''Returns a new DataFrame where the virtual column is turned into an in memory numpy array.

        Example:

        >>> x = np.arange(1,4)
        >>> y = np.arange(2,5)
        >>> df = vaex.from_arrays(x=x, y=y)
        >>> df['r'] = (df.x**2 + df.y**2)**0.5 # 'r' is a virtual column (computed on the fly)
        >>> df = df.materialize('r')  # now 'r' is a 'real' column (i.e. a numpy array)

        :param inplace: {inplace}
        '''
        df = self.trim(inplace=inplace)
        virtual_column = _ensure_string_from_expression(virtual_column)
        if virtual_column not in df.virtual_columns:
            raise KeyError('Virtual column not found: %r' % virtual_column)
        ar = df.evaluate(virtual_column, filtered=False)
        del df[virtual_column]
        df.add_column(virtual_column, ar)
        return df
Returns a new DataFrame where the virtual column is turned into an in memory numpy array.

        Example:

        >>> x = np.arange(1,4)
        >>> y = np.arange(2,5)
        >>> df = vaex.from_arrays(x=x, y=y)
        >>> df['r'] = (df.x**2 + df.y**2)**0.5 # 'r' is a virtual column (computed on the fly)
        >>> df = df.materialize('r')  # now 'r' is a 'real' column (i.e. a numpy array)

        :param inplace: {inplace}