python - 在多列 Pandas 上加入 2 个数据框

Question

考虑 2 个数据帧，需要通过 2 个唯一列(idA、idB)连接 2 个数据帧，并计算它们的列距离之和.顺便说一下 (idA,idB) 等于 (idB,idA)，所以他们的 Distance 必须相加

In [1]: df1 = pd.DataFrame({'idA': ['1', '2', '3', '2'],
   ...:                     'idB': ['1', '4', '8', '1'],
   ...:                     'Distance': ['0.727273', '0.827273', '0.127273', '0.927273']},
   ...:                     index=[0, 1, 2, 3])
   ...: 

In [2]: df2 = pd.DataFrame({'idA': ['1', '5', '2', '5'],
   ...:                     'idB': ['2', '1', '4', '7'],
   ...:                     'Distance': ['0.11', '0.1', '3.0', '0.8']},
   ...:                      index=[4, 5, 6, 7])

输出必须是这样的:

    Sum_Distance    idA idB
  0  0.727273       1   1
  1  3.827273       2   4  <-- 2,4 = 3.0 + 2,4 = 0.827273
  2  0.127273       3   8
  3  1.037273       2   1  <-- 2,1 = 0.927273 + 1,2 = 0.11
  4  0.1            5   1
  5  0.8            5   7

帮助找到使用 Pandas/Spark 的方法。

Answer 1

首先将两列都转换为数字，然后使用 add与 set_index用于每行对齐和排序每对列:

df1['Distance'] = df1['Distance'].astype(float)      
df2['Distance'] = df2['Distance'].astype(float)  

#if some data are not parseable convert them to NaNs 
#df1['Distance'] = pd.to_numeric(df1['Distance'], errors='coerce')      
#df2['Distance'] = pd.to_numeric(df2['Distance'], errors='coerce')  

df1[['idA','idB']] = np.sort(df1[['idA','idB']], axis=1)
df2[['idA','idB']] = np.sort(df2[['idA','idB']], axis=1) 

print (df1)
   Distance idA idB
0  0.727273   1   1
1  0.827273   2   4
2  0.127273   3   8
3  0.927273   1   2

print (df2)
   Distance idA idB
4      0.11   1   2
5      0.10   1   5
6      3.00   2   4
7      0.80   5   7   

---

df3=df1.set_index(['idA','idB']).add(df2.set_index(['idA','idB']),fill_value=0).reset_index()
print (df3)
  idA idB  Distance
0   1   1  0.727273
1   1   2  1.037273
2   1   5  0.100000
3   2   4  3.827273
4   3   8  0.127273
5   5   7  0.800000

另一种解决方案 concat和 groupby使用聚合 sum:

df3 = pd.concat([df1, df2]).groupby(['idA','idB'], as_index=False)['Distance'].sum()
print (df3)
  idA idB  Distance
0   1   1  0.727273
1   1   2  1.037273
2   1   5  0.100000
3   2   4  3.827273
4   3   8  0.127273
5   5   7  0.800000