Pandas pivot 表中是否有function 添加多列的差異？

Question

我有以下 pandas DataFrame：

df = pd.DataFrame({"A": ["foo", "foo", "foo", "foo", "foo",
                         "bar", "bar", "bar", "bar",'foo' ],
                   "B": ["one", "one", "one", "two", "two",
                         "one", "one", "two", "two", 'two'],
                   "C": ["small", "large", "large", "small",
                         "small", "large", "small", "small",
                         "large", 'large'],
                   "D": [1, 2, 2, 3, 3, 4, 5, 6, 7,8],
               })

使用以下 output：

print(df)

    A   B   C       D
0   foo one small   1
1   foo one large   2
2   foo one large   2
3   foo two small   3
4   foo two small   3
5   bar one large   4
6   bar one small   5
7   bar two small   6
8   bar two large   7
9   foo two large   8

然后我正在做一個 pivot 表，如下所示：

table = pd.pivot_table(df, values='D', index=['A'],
                    columns=['B','C'])

使用以下 output：

print(table)

B   one             two
C   large   small   large   small
A               
bar   4      5       7        6
foo   2      1       8        3

我如何為one和two添加large和small （ large - small ）之間的diff （下表中的差異）？ 預期的 output 將是：

B   one                 two
C   large   small diff  large   small difff
A               
bar   4        5   -1     7       6    1
foo   2        1    1     8       3    5

我看到了一些以前的答案，但只處理了 1 列。 此外，理想情況下將使用aggfunc完成

另外，如何將表格重新轉換為初始格式？ 預計 output 將是：

  A   B   C     D 
0  foo one small 1 
1  foo one large 2 
2  foo one large 2 
3  foo two small 3 
4  foo two small 3 
5  bar one large 4 
6  bar one small 5 
7  bar two small 6 
8  bar two large 7 
9  foo two large 8 
10 bar one diff -1 
11 bar two diff 1 
12 foo one diff 1 
13 foo two diff 5

在此先感謝您的幫助！

Answer 1

diffs = (table.groupby(level="B", axis="columns")
              .diff(-1).dropna(axis="columns")
              .rename(columns={"large": "diff"}, level="C"))

new = table.join(diffs).loc[:, table.columns.get_level_values("B").unique()]

• 按列的“B”級別分組（“一”、“二”...）
• 從左到右取差 (diff(-1))
  • 即，計算“大 - 小”值
• 因為 small 旁邊沒有任何東西，所以都是 NaN，放棄它
• 重命名實際上現在存在差異的“大”
• 加入數據透視表並恢復“一”、“二”的原始順序

要得到

>>> new

B     one              two
C   large small diff large small diff
A
bar     4     5   -1     7     6    1
foo     2     1    1     8     3    5