Series.filter?
Is there an equivalent to DataFrame.filter(regex=...) for Series? I don't see anything in 0.9.0, and I'm not somewhere I can check and upgrade easily. Use case, using iterrows returns a Series for each row, and I can't pre-filter the DataFrame because the regex criterion is dependent on the index. Ie., for row index = d I want to use [X1, X2, ..., Xd]. I'm sure there's a workaround but filter could be handy here.
