Get data for each ridgeplot for the variable.

def ridgeplot(self, mult):
        """Get data for each ridgeplot for the variable."""
        xvals, yvals, pdfs, colors = [], [], [], []
        for y, *_, values, color in self.iterator():
            yvals.append(y)
            colors.append(color)
            values = values.flatten()
            density, lower, upper = _fast_kde(values)
            xvals.append(np.linspace(lower, upper, len(density)))
            pdfs.append(density)

        scaling = max(j.max() for j in pdfs)
        for y, x, pdf, color in zip(yvals, xvals, pdfs, colors):
            y = y * np.ones_like(x)
            yield x, y, mult * pdf / scaling + y, color