Transform all the variables that map onto the x and y scales.

        Parameters
        ----------
        data    : dataframe
        trans_x : function
            Transforms x scale mappings
            Takes one argument, either a scalar or an array-type
        trans_y : function
            Transforms y scale mappings
            Takes one argument, either a scalar or an array-type

def transform_position(data, trans_x=None, trans_y=None):
        """
        Transform all the variables that map onto the x and y scales.

        Parameters
        ----------
        data    : dataframe
        trans_x : function
            Transforms x scale mappings
            Takes one argument, either a scalar or an array-type
        trans_y : function
            Transforms y scale mappings
            Takes one argument, either a scalar or an array-type
        """
        # Aesthetics that map onto the x and y scales
        X = {'x', 'xmin', 'xmax', 'xend', 'xintercept'}
        Y = {'y', 'ymin', 'ymax', 'yend', 'yintercept'}

        if trans_x:
            xs = [name for name in data.columns if name in X]
            data[xs] = data[xs].apply(trans_x)

        if trans_y:
            ys = [name for name in data.columns if name in Y]
            data[ys] = data[ys].apply(trans_y)

        return data