python - 来自 groupby 的 Pandas 累积差异

Question

我需要计算从 MultiIndex 级别开始的差异，以计算从级别开始的衰减。我的示例输入和输出将如下所示:

               values
place time     
A     a           120
      b           100
      c            90
      d            50
B     e            11
      f            12
      g            10
      h             9

               values

A     a           NaN
      b           -20
      c           -30
      d           -70
B     e           Nan
      f            +1
      g            -1
      h            -2

我可以使用 grouby 来获取关卡中连续单元格之间的差异:

df.groupby(level=0)['values'].diff()

但这不是我想要的!

唉，接受的答案不是我想要的。我有一个更好的例子:

arrays = [np.array(['bar', 'bar', 'bar', 'foo', 'foo', 'foo']),
          np.array(['one', 'two', 'three', 'one', 'two', 'three'])]
df = pd.DataFrame([1000, 800, 500, 800, 400, 200], index=arrays)

   bar one    1000
       two     800
       three   500
   foo one     800
       two     400
       three   200

    expected_result = pd.DataFrame([Nan, -200, -500, Nan, -400, -600], index=arrays)

   bar one      Nan
       two     -200
       three   -500
   foo one     Nan 
       two     -400
       three   -600

但是 df.groupby(level=0).diff().cumsum() 的结果是:

pd.DataFrame([Nan, -200, -500, Nan, -900, -1100], index=arrays)

   bar one      Nan
       two     -200
       three   -500
   foo one      Nan 
       two     -900
       three   -1100

Answer 1

你在寻找 cumsum 之后吗？

df.groupby(level=0)['values'].diff().cumsum()