我使用的是Pandas 1.51，我试图通过使用FixedForwardWindowIndexer来获得滚动窗口中 Dataframe 中每一行的排名，但我无法理解结果。

df = pd.DataFrame({"X":[9,3,4,5,1,2,8,7,6,10,11]})
window_size = 5
indexer = pd.api.indexers.FixedForwardWindowIndexer(window_size=window_size)
df.rolling(window=indexer).rank(ascending=False)

结果：

X
0   5.0
1   4.0
2   1.0
3   2.0
4   3.0
5   1.0
6   1.0
7   NaN
8   NaN
9   NaN
10  NaN

据我估计，它应该看起来像：

X
0   1.0 # based on the window [9,3,4,5,1], 9 is ranked 1st w/ascending = False
1   3.0 # based on the window [3,4,5,1,2], 3 is ranked 3rd
2   3.0 # based on the window [4,5,1,2,8], 4 is ranked 3rd
3   3.0 # etc
4   5.0
5   5.0
6   3.0
7   NaN
8   NaN
9   NaN
10  NaN

我是基于一个向后看的窗口，它工作得很好：

>>> df.rolling(window_size).rank(ascending=False)
      X
0   NaN
1   NaN
2   NaN
3   NaN
4   5.0
5   4.0
6   1.0
7   2.0
8   3.0
9   1.0
10  1.0

任何帮助都是最受欢迎的。