python - Pandas - 将具有多列的数据框 reshape /转换为单列值

Question

我有一个 pandas 数据框，其中年份作为列，国家/地区作为行名:

Country       | 1960 | 1961 | 1962 | 1963
-----------------------------------------
United States | 1000 | 2000 | 3000 | 4000
-----------------------------------------
Argentina     | 1000 | 2000 | 3000 | 4000
-----------------------------------------

我想把它改造成:

Country       | Year | Value
-----------------------------
Unites States | 1960 | 1000
Unites States | 1961 | 2000
Unites States | 1962 | 3000
Unites States | 1963 | 4000
Argentina     | 1960 | 1000
Argentina     | 1961 | 2000
Argentina     | 1962 | 3000
Argentina     | 1963 | 4000

我不确定需要应用哪些拆分、排序或分组操作才能实现此目标。

谢谢!

Answer 1

举个完整的例子，

In [1]: df = pd.DataFrame([['United States', 1000, 2000, 3000, 4000],
                           ['Argentina', 1000, 2000, 3000, 4000]],
                          columns=['Country', 1960, 1961, 1962, 1963])

In [2]: df.set_index('Country', inplace=True)
In [3]: df = df.stack().reset_index()
In [4]: df.columns = ['Country', 'Year', 'Value']

产量

         Country  Year  Value
0  United States  1960   1000
1  United States  1961   2000
2  United States  1962   3000
3  United States  1963   4000
4      Argentina  1960   1000
5      Argentina  1961   2000
6      Argentina  1962   3000
7      Argentina  1963   4000

---

要摆脱索引列并使用 Country 列作为索引，您可以使用

In [3]: df = df.stack().reset_index(1)
In [4]: df.columns = ['Year', 'Value']

产生

               Year  Value
Country                   
United States  1960   1000
United States  1961   2000
United States  1962   3000
United States  1963   4000
Argentina      1960   1000
Argentina      1961   2000
Argentina      1962   3000
Argentina      1963   4000