def reshape_pivot(df_in):
    """
    Reduce df to crucial subset then pivot on cases and genes.
    """
    df = (df_in[['case_barcode', 'Hugo_Symbol', 'mutation_count']]
              .copy()
              .pivot(index='case_barcode', columns='Hugo_Symbol', values='mutation_count')
              .fillna(0)
              .astype(int))
    
    return df