Python Multi-Index：使用 2 级索引 DataFrame 查找坐标

Question

我有一个带有多索引索引和列的空 DataFrame。我还有作为二级索引坐标的字符串列表。由于我所有的二级索引都是唯一的，我希望用我的字符串列表找到坐标和输入值。看看下面的例子

df=
       DNA      Cat2                                 ....   
       Item     A   B   C   D   E   F   F   H   I   J   
DNA   Item
Cat2  A         0   0   0   0   0   0   0   0   0   0 
      B         0   0   0   0   0   0   0   0   0   0 
      C         0   0   0   0   0   0   0   0   0   0 
      D         0   0   0   0   0   0   0   0   0   0 
      E         0   0   0   0   0   0   0   0   0   0 
      F         0   0   0   0   0   0   0   0   0   0 
....

str_cord = [(A,B),(A,H),(A,I),(B,H),(B,I),(H,I)]
#and my output should be like below.

df_result=
       DNA      Cat2                                 ....   
       Item     A   B   C   D   E   F   F   H   I   J   
DNA   Item
Cat2  A         0   1   0   0   0   0   0   1   1   0 
      B         0   0   0   0   0   0   0   1   1   0 
      C         0   0   0   0   0   0   0   0   0   0 
      D         0   0   0   0   0   0   0   0   0   0 
      E         0   0   0   0   0   0   0   0   0   0 
      F         0   0   0   0   0   0   0   0   0   0 
      H         0   0   0   0   0   0   0   0   1   0
....

它看起来有点复杂，但我想做的就是使用我的 str_cord[0] 作为 df_result 的坐标。我尝试使用 .loc，但似乎我需要输入 1 级索引。我正在寻找不必输入 Multi-Index level1 并使用 level2 字符串查找坐标的方式。希望这是有道理的，并在此先感谢！ （哦，数据本身很大，所以尽可能的高效）

Answer 1

你可以使用：

for i, j in str_cord:
    idx = pd.IndexSlice
    df.loc[idx[:, i], idx[:, j]] = 1

示例：

L = list('ABCDEFGHIJ')
mux = pd.MultiIndex.from_product([['Cat1','Cat2'], L])

df = pd.DataFrame(0, index=mux, columns=mux)
print (df)
       Cat1                            Cat2                           
          A  B  C  D  E  F  G  H  I  J    A  B  C  D  E  F  G  H  I  J
Cat1 A    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     B    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     C    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     D    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     E    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     F    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     G    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     H    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     I    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     J    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
Cat2 A    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     B    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     C    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     D    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     E    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     F    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     G    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     H    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     I    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     J    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0

---

str_cord = [('A','B'),('A','H'),('A','I'),('B','H'),('B','I'),('H','I')]

for i, j in str_cord:
    idx = pd.IndexSlice
    df.loc[idx[:, i], idx[:, j]] = 1

---

print (df)
       Cat1                            Cat2                           
          A  B  C  D  E  F  G  H  I  J    A  B  C  D  E  F  G  H  I  J
Cat1 A    0  1  0  0  0  0  0  1  1  0    0  1  0  0  0  0  0  1  1  0
     B    0  0  0  0  0  0  0  1  1  0    0  0  0  0  0  0  0  1  1  0
     C    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     D    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     E    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     F    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     G    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     H    0  0  0  0  0  0  0  0  1  0    0  0  0  0  0  0  0  0  1  0
     I    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     J    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
Cat2 A    0  1  0  0  0  0  0  1  1  0    0  1  0  0  0  0  0  1  1  0
     B    0  0  0  0  0  0  0  1  1  0    0  0  0  0  0  0  0  1  1  0
     C    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     D    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     E    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     F    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     G    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     H    0  0  0  0  0  0  0  0  1  0    0  0  0  0  0  0  0  0  1  0
     I    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0
     J    0  0  0  0  0  0  0  0  0  0    0  0  0  0  0  0  0  0  0  0