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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 aggregated_relevant_items(raw_df):
 """ Aggragation for calculate mean and std. """

    df = (
        raw_df[['idSegmento', 'idPlanilhaItens', 'VlUnitarioAprovado']]
        .groupby(by=['idSegmento', 'idPlanilhaItens'])
        .agg([np.mean, lambda x: np.std(x, ddof=0)])
    )
    df.columns = df.columns.droplevel(0)
    return (
        df
        .rename(columns={'<lambda>': 'std'})
    )