Pandas：將日期跨 x 軸映射到 CSV 中的 y 軸

Question

給定以下 CSV 文件（在 DataFrame 中通過pandas.from_csv(...) ：

+---------+----------+----------+----------+
| country | 02/11/20 | 03/11/20 | 04/11/20 |
+---------+----------+----------+----------+
| Norway  |     5100 |     5200 |     5300 |
| Sweden  |     6100 |     6200 |     6300 |
| Finland |     4100 |     4200 |     4300 |
+---------+----------+----------+----------+

如何在 python 中使用pandas將其轉換為以下內容：

+----------+---------+------------+
|   date   | country | population |
+----------+---------+------------+
| 02/11/20 | Norway  |       5100 |
| 03/11/20 | Norway  |       5200 |
| 04/11/20 | Norway  |       5300 |
| 02/11/20 | Sweden  |       6100 |
| 03/11/20 | Sweden  |       6200 |
| 04/11/20 | Sweden  |       6300 |
| 02/11/20 | Finland |       4100 |
| 03/11/20 | Finland |       4200 |
| 04/11/20 | Finland |       4300 |
+----------+---------+------------+

所以基本上將 x 軸上的日期映射到 y 軸。

Answer 1

嘗試：

df.melt('country', var_name='date', value_name='population')

輸出：

     country      date  population
0   Norway    02/11/20        5100
1   Sweden    02/11/20        6100
2   Finland   02/11/20        4100
3   Norway    03/11/20        5200
4   Sweden    03/11/20        6200
5   Finland   03/11/20        4200
6   Norway    04/11/20        5300
7   Sweden    04/11/20        6300
8   Finland   04/11/20        4300