Select features to plot.

        feature_index is always used as the filter and
        if filter_names is supplied, a new feature_index
        is computed from those names.

def _select_features_to_plot(self, X):
        """
        Select features to plot.

        feature_index is always used as the filter and
        if filter_names is supplied, a new feature_index
        is computed from those names.
        """
        if self.feature_index:
            if self.feature_names:
                raise YellowbrickWarning(
                    'Both feature_index and feature_names '
                    'are specified. feature_names is ignored'
                )
            if (min(self.feature_index) < 0
                    or max(self.feature_index) >= X.shape[1]):
                raise YellowbrickValueError('Feature index is out of range')
        elif self.feature_names:
            self.feature_index = []
            features_list = self.features_.tolist()
            for feature_name in self.feature_names:
                try:
                    self.feature_index.append(
                        features_list.index(feature_name)
                    )
                except ValueError:
                    raise YellowbrickValueError(
                        '{} not in labels'.format(feature_name)
                    )