Draws a histogram with the reference value for binning as vertical
        lines.

        Parameters
        ----------
        y : an array of one dimension or a pandas Series

def draw(self, y, **kwargs):
        """
        Draws a histogram with the reference value for binning as vertical
        lines.

        Parameters
        ----------
        y : an array of one dimension or a pandas Series
        """

        # draw the histogram
        hist, bin_edges = np.histogram(y, bins=self.bins)
        self.bin_edges_ = bin_edges
        self.ax.hist(y, bins=self.bins, color=kwargs.pop("color", "#6897bb"), **kwargs)

        # add vetical line with binning reference values
        plt.vlines(bin_edges,0,max(hist),colors=kwargs.pop("colors", "r"))