Fix uncomparable values in SimpleImputer tie-breaking strategy #31820
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When encountering uncomparable types, SimpleImputer's 'min' strategy previously raised an error. This commit resolves the issue by selecting the value with the smallest hash of its pickled representation as a fallback. Fix scikit-learn#31717
sklearn/impute/_base.py
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| return min(items) | ||
| except TypeError as e: | ||
| if "'<' not supported between" in str(e): | ||
| return min(items, key=lambda x: murmurhash3_32(pickle.dumps(x))) |
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I wonder if it's not a bit overkill. For the use case of SimpleImputer, I believe that using the string representation of objects would be fine. It's deterministic across versions, os, envs... for usual types (int, float, str, None). It's not on more complex objects but I don't think that we expect complex objects to be passed to SimpleImputer.
| return min(items, key=lambda x: murmurhash3_32(pickle.dumps(x))) | |
| return min(items, key=str) |
What do you think ?
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I thought of that too but I am bugged by the 1 out of a million case where there is a tie between None and 'None' that is shuffle-sensitive:
In [1]: min([None, 'None'], key=str)
In [2]: min(['None', None], key=str)
Out[2]: 'None'repr does not fail in that case but it may in others.
Actually, we do not really need the hash, the pickle dumped string should be unique.
return min(items, key=lambda x: pickle.dumps(x))Is that better? Still needs pickle though...
Actually, that's where the other PR comes in handy, using the type breaks the tie.
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It's actually the same for 1 and "1" and so on which is more likely to happen.
I was undecided between pickle.dumps(x) and (str(type(x), str(x)), but a quick benchmark showed that the latter is much faster, so I'm in favor of choosing this one.
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Maybe another reason to not rely on pickle is that IIRC there are very little promises about the contents of a pickle with respect to the Python version (I think you'd have to select an explicit version of the protocol?). Generally it feels like using pickle is somehow "too complicated"
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I directly pushed a commit to use (str(type(x)), str(x)) as key. LGTM.
@betatim is this solution fine for you ?
jeremiedbb
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Sorry, I was off, I could not implement the requests. let me know if there is anything more I can do. |
Fixes #31717
When encountering uncomparable types, SimpleImputer's 'min' strategy previously raised an error. This commit resolves the issue by selecting the value with the smallest hash of its pickled representation as a fallback.
The pickled value is used because some special values such as
Noneare not handled natively by murmurhash.