A map method to work with many columns
Hi,

I would like to map a function expecting N arguments to a DataFrame of N columns. Today to do that I do:

```python
df = pd.DataFrame({"A": [1, 2, 3, 4], "B": [5, 6, 7, 8]})
def f(x,y):
     return x*y

df[['A', 'B']].apply(lambda x: f(*x), axis=1) 
```
So the `map` method for DataFrame would be:

```python
def map(self, f):
    return self.apply(lambda x: f(*x), axis=1)
```
if I am right. Then `df.map(f)` would produce a Serie.

Note that with 1 colummn and a 1 argument function `map` would work as `numpy.map` does.

Thanks,

Olivier.

ps: I edited this post after the talk I had with Tom, so it must seem strange now :smiley: 