pydata/pandas — pull request #5187 by jreback (2013-10-11 23:10:20+00:00)
Title: BUG: Allow duplicate indices when performing operations that align (GH5185)

closes #5185

```
In [1]: df1 = DataFrame([1, 2, 3, 4, 5], index=[1, 2, 1, 2, 3])

In [2]: df2 = DataFrame([1, 2, 3], index=[1, 2, 3])

In [3]: df1-df2
Out[3]:
0
1 0
1 2
2 0
2 2
3 2

In [4]: df1.sub(df2)
Out[4]:
0
1 0
1 2
2 0
2 2
3 2
```