2014-02-27 23:37 GMT+01:00 Joel Nothman <joel.noth...@gmail.com>:
> I think it would be nice if the FeatureUnion makes it easy to extract
> only certain parts of the input for each transformer.
> https://github.com/scikit-learn/scikit-learn/issues/2034 intends to
> cover this issue, but we haven't resolved a clean API.
>
> Suggestions are welcome!
I hope you don't mind me replying here: I think this can be resolved
by custom transformers that pass through a user-specified set of
columns. My preferred way of implementing that would be a generic,
stateless transformer class that just runs a function on X in
transform and returns the result. If this transformer doesn't do input
validation, you could make a union
make_pipeline(FunctionTransformer(extract_description_terms),
TfidfTransformer())
∪
make_pipeline(FunctionTransformer(extract_portrait_pixels), PCA())
and feed this filenames, or dicts, or whatever. The original problem
of letting though only some columns is then
def even_columns(X, *args):
X = np.asarray(X)
return X[:, ::2]
FunctionTransformer(even_columns)
And of course, these things are more generally useful for inserting a
simple function in the middle of a pipeline.
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