docs: def cond_entropy(x, y, bins_y=None, bins_xy=None, method='nearest-neighbors', units='bits'):
      '''
      compute the conditional entropy H(X|Y).
  
      method:     'nearest-neighbors', 'gaussian', or 'bin'
                  if 'bin' need to provide bins_y, and bins_xy
      units:      'bits' or 'nats'
      '''
      HXY = entropy(data=np.concatenate([x, y], axis=1), bins=bins_xy, method=method, units=units)
      HY  = entropy(data=y, bins=bins_y, method=method, units=units)
  
      return HXY - HY