def _build_data_meta(self, dataset_data_list, df):
        merged_data_metadata = {}
        # for sanity check if list has items
        if dataset_data_list:
            # meta should be the same for every individual Dataset
            # request, just take the first one
            merged_data_metadata = dataset_data_list[0].meta.copy()

            # set the start_date and end_date to
            # the actual values we got back from data
            num_rows = len(df.index)
            if num_rows > 0:
                merged_data_metadata['start_date'] = df.index[0].date()
                merged_data_metadata['end_date'] = df.index[num_rows - 1].date()

            # remove column_index if it exists because this would be per request data
            merged_data_metadata.pop('column_index', None)

            # don't use self.column_names to prevent metadata api call
            # instead, get the column_names from the dataset_data_objects
            merged_data_metadata['column_names'] = self._merged_column_names_from(dataset_data_list)
        return merged_data_metadata
dataset/ETHPy150Open quandl/quandl-python/quandl/model/merged_dataset.py/MergedDataset._build_data_meta/original