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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def construct_FAO_ontology():
 """ Construct FAO variable ontology for use with Eidos. """

    df = pd.read_csv("south_sudan_data_fao.csv")
    gb = df.groupby("Element")

    d = [
        {
            "events": [
                {
                    k: [
                        {e: [process_variable_name(k, e)]}
                        for e in list(set(gb.get_group(k)["Item"].tolist()))
                    ]
                }
                for k in gb.groups.keys()
            ]
        }
    ]

    yaml = YAML()
    yaml.default_flow_style = False

    with open("fao_variable_ontology.yml", "w") as f:
        yaml.dump(d, f)