docs: def plot_ic_by_group(ic_group, ax=None):
      """
      Plots Spearman Rank Information Coefficient for a given factor over
      provided forward returns. Separates by group.
  
      Parameters
      ----------
      ic_group : pd.DataFrame
          group-wise mean period wise returns.
      ax : matplotlib.Axes, optional
          Axes upon which to plot.
  
      Returns
      -------
      ax : matplotlib.Axes
          The axes that were plotted on.
      """
      if ax is None:
          f, ax = plt.subplots(1, 1, figsize=(18, 6))
      ic_group.plot(kind='bar', ax=ax)
  
      ax.set(title="Information Coefficient By Group", xlabel="")
      ax.set_xticklabels(ic_group.index, rotation=45)
  
      return ax