拆分一個多指標數據幀的基礎上另據幀

Question

假設你有一個多指標數據幀

x y z 
a 1 0 1 2 
    2 3 4 5 
b 1 0 1 2 
    2 3 4 5 
    3 6 7 8 
c 1 0 1 2 
    2 0 4 6 

現在你有另一個數據幀是

col1 col2 
0 a 1 
1 b 1 
2 b 3 
3 c 1 
4 c 2 

你如何基於上面的一個分裂的多指標數據幀？

Answer 1

使用loc通過tuple S：

df = df1.loc[df2.set_index(['col1','col2']).index.tolist()] 
print (df) 
    x y z 
a 1 0 1 2 
b 1 0 1 2 
    3 6 7 8 
c 1 0 1 2 
    2 0 4 6 

---

df = df1.loc[[tuple(x) for x in df2.values.tolist()]] 
print (df) 
    x y z 
a 1 0 1 2 
b 1 0 1 2 
    3 6 7 8 
c 1 0 1 2 
    2 0 4 6 

或者join：

df = df2.join(df1, on=['col1','col2']).set_index(['col1','col2']) 
print (df) 
      x y z 
col1 col2   
a 1  0 1 2 
b 1  0 1 2 
    3  6 7 8 
c 1  0 1 2 
    2  0 4 6 

Answer 2

你也可以做到這一點使用的多指標重新索引方法https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.reindex.html

## Recreate your dataframes 
tuples = [('a', 1), ('a', 2), 
       ('b', 1), ('b', 2), 
       ('b', 3), ('c', 1), 
       ('c', 2)] 

data = [[1, 0, 1, 2], 
     [2, 3, 4, 5], 
     [1, 0, 1, 2], 
     [2, 3, 4, 5], 
     [3, 6, 7, 8], 
     [1, 0, 1, 2], 
     [2, 0, 4, 6]] 

idx = pd.MultiIndex.from_tuples(tuples, names=['index1','index2']) 
df= pd.DataFrame(data=data, index=idx) 

df2 = pd.DataFrame([['a', 1], 
        ['b', 1], 
        ['b', 3], 
        ['c', 1], 
        ['c', 2]]) 

# Answer Question 
idx_subset = pd.MultiIndex.from_tuples([(a, b) for a, b in df2.values], names=['index1', 'index2']) 
out = df.reindex(idx_subset) 
print(out) 
        0 1 2 3 
index1 index2    
a  1  1 0 1 2 
b  1  1 0 1 2 
     3  3 6 7 8 
c  1  1 0 1 2 
     2  2 0 4 6 

Answer 3

只需用isin

df[df.index.isin(list(zip(df2['col1'],df2['col2'])))] 


Out[342]: 
       0 1 2 3 
index1 index2    
a  1  1 0 1 2 
b  1  1 0 1 2 
     3  3 6 7 8 
c  1  1 0 1 2 
     2  2 0 4 6