======================================================
Data That Only Makes Sense In Relation To Another File
======================================================

Scenario
========

The ``source_data_url`` gives you access to one data file, but you need to
access one or more other files to make sense of your source data.

File Fetching Solution
======================

You can access the file fetching methods yourelf to load the data from as many
secondary files as you want. For instance, for a secondary TSV file, you can
do:

.. code-block:: Python

    from kf_lib_data_ingest.common.file_retriever import FileRetriever
    from kf_lib_data_ingest.common.io import read_df

    file_df = read_df(
        FileRetriever().get("<URL for your TSV file>")
    )

Keep in mind that ``in_col`` arguments in the :ref:`operations list
<Extract-Mapping>` can only read from either the primary source data file
referenced by :ref:`source_data_url<Fetching-the-Data>` or the DataFrame
returned by the :ref:`do_after_read<Extract-Preprocessing>` function.