docs: def _index_into(self, idx, data):
          """
          Attempts to get the column from the data using the specified index, raises an
          exception if this is not possible from this point in the stack.
          """
          try:
              if is_dataframe(data):
                  # Assume column indexing
                  return data[idx]
              # Otherwise assume numpy array-like indexing
              return data[:,idx]
          except Exception as e:
              raise IndexError(
                  "could not index column '{}' into type {}: {}".format(
                      self.columns, data.__class__.__name__, e
              ))