groupby diff

def apply_diff_func(df):
    df['difference'] = df['col'].diff()
    return df

outputdf = df.groupby('storeid').apply(apply_diff_func)


def apply_shift_func(df):
    df['shifted'] = df['col'].shift(1)
    df['difference'] = df['col'] - df['difference']
    return df

outputdf = df.groupby('storeid').apply(apply_diff_func)