ContinuumIO/blaze — pull request #512 by mrocklin (2014-08-25 22:13:05+00:00)
Title: Merge repeated columns

Fixes #510 cc @chdoig

This does two things.

1. It raises an error if `merge` is called with overlapping column names
2. `transform` from `dplyr` will overwrite columns by default.

```Python
In [1]: from blaze import *

In [2]: df = DataFrame([[1, 'Alice', 100],
[2, 'Bob', -200],
[3, 'Charlie', 300],
[4, 'Dennis', 400],
[5, 'Edith', -500]],
columns=['id', 'name', 'amount'])

In [3]: t = Table(df)

In [4]: t
Out[4]:
id name amount
0 1 Alice 100
1 2 Bob -200
2 3 Charlie 300
3 4 Dennis 400
4 5 Edith -500

In [5]: transform(t, amount=-t.amount)
Out[5]:
id name amount
0 1 Alice -100
1 2 Bob 200
2 3 Charlie -300
3 4 Dennis -400
4 5 Edith 500
```