要计算按小时计算的Dataframe列的天数，可以使用以下代码示例来解决问题：

import pandas as pd

# 创建示例数据
data = {'date': pd.date_range(start='2022-01-01 00:00:00', end='2022-01-03 23:00:00', freq='H')}
df = pd.DataFrame(data)

# 计算天数
df['day'] = df['date'].dt.floor('D')

# 输出结果
print(df)

输出结果如下：

                  date        day
0  2022-01-01 00:00:00 2022-01-01
1  2022-01-01 01:00:00 2022-01-01
2  2022-01-01 02:00:00 2022-01-01
3  2022-01-01 03:00:00 2022-01-01
4  2022-01-01 04:00:00 2022-01-01
5  2022-01-01 05:00:00 2022-01-01
6  2022-01-01 06:00:00 2022-01-01
7  2022-01-01 07:00:00 2022-01-01
8  2022-01-01 08:00:00 2022-01-01
9  2022-01-01 09:00:00 2022-01-01
10 2022-01-01 10:00:00 2022-01-01
11 2022-01-01 11:00:00 2022-01-01
12 2022-01-01 12:00:00 2022-01-01
13 2022-01-01 13:00:00 2022-01-01
14 2022-01-01 14:00:00 2022-01-01
15 2022-01-01 15:00:00 2022-01-01
16 2022-01-01 16:00:00 2022-01-01
17 2022-01-01 17:00:00 2022-01-01
18 2022-01-01 18:00:00 2022-01-01
19 2022-01-01 19:00:00 2022-01-01
20 2022-01-01 20:00:00 2022-01-01
21 2022-01-01 21:00:00 2022-01-01
22 2022-01-01 22:00:00 2022-01-01
23 2022-01-01 23:00:00 2022-01-01
24 2022-01-02 00:00:00 2022-01-02
25 2022-01-02 01:00:00 2022-01-02
26 2022-01-02 02:00:00 2022-01-02
27 2022-01-02 03:00:00 2022-01-02
28 2022-01-02 04:00:00 2022-01-02
29 2022-01-02 05:00:00 2022-01-02
30 2022-01-02 06:00:00 2022-01-02
31 2022-01-02 07:00:00 2022-01-02
32 2022-01-02 08:00:00 2022-01-02
33 2022-01-02 09:00:00 2022-01-02
34 2022-01-02 10:00:00 2022-01-02
35 2022-01-02 11:00:00 2022-01-02
36 2022-01-02 12:00:00 2022-01-02
37 2022-01-02 13:00:00 2022-01-02
38 2022-01-02 14:00:00 2022-01-02
39