Option to Raise Exception on Unmapped Value in Series.map

Add a flag (or extend na_action) to raise an exception in Series.map if a value is not successfully mapped (ie in the case where arg is a dict.

[cancan101]

If I were do this:

Series(['a', 'b']).map({'a': 1, 'b': 3})

my return type is of int64 and everything is mapped. However for this:

Series(['a', 'b ']).map({'a': 1, 'b': 3}) # note space

my return type is floatX and there is a nan. Instead this is a “mistake” and I would have preferred an exception to be raised.

I could assert that the type is int (brittle and just works for ints) or perhaps check all of the unique values in advance to make sure they are a subset of the mapping arg keys (require another pass over data).

[bollard]

Quite the 6-year necroraise, but little bump that would be really useful to have an na_action="raise" on Series.map

A workaround for the moment is to (re)define __missing__ to raise, i.e.

class WillRaise(dict):
    def __missing__(self, key):
        raise KeyError(key)

mapping = WillRaise({"Foo": 1})
pd.Series(["Foo", "Bar"]).map(mapping) # KeyError: 'Bar'