def preu_mitja(df, t, g, v):
    df2 = df[(df['Talla'] == t) & (df['Gènere'] == g) & (df['Venedor'] == v)]
    if len(df2) == 0:
        return 0.0
    else:
        preu_total = df2['Preu'].sum()
        unitats_total = df2['Unitats'].sum()
        return preu_total / unitats_total