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`SimpleImputer.fit` strange behavior with `median` and `most_frequent` strategies #787

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abduhbm opened this issue Feb 4, 2021 · 0 comments · May be fixed by #788

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abduhbm commented Feb 4, 2021 •

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What happened:
SimpleImputer.fit with median and most_frequent strategies on frames compute different results comparing to scikit-learn.

What you expected to happen:
They should have consistent results with sklearn.impute.SimpleImputer.

Minimal Complete Verifiable Example:

df = pd.DataFrame({"A": [1, 1, np.nan, np.nan, 2, 2]})
# This should return the smallest value
b = dask_ml.impute.SimpleImputer(strategy="most_frequent", fill_value=None)
b.fit(df)
b.statistics_
>>> A    2.0
>>> dtype: float64

c = sklearn.impute.SimpleImputer(strategy="most_frequent", fill_value=None)
c.fit(df)
c.statistics_
>>> array([1.])

With median:

df = pd.DataFrame({"A": [1, 1, np.nan, np.nan, 2, 2]})
df = dd.from_pandas(df, 2)
b = dask_ml.impute.SimpleImputer(strategy="median", fill_value=None)
b.fit(df)
b.statistics_
>>> A    1.0
>>> dtype: float64

c = sklearn.impute.SimpleImputer(strategy="median", fill_value=None)
c.fit(df)
c.statistics_
>>> array([1.5])

Environment:

Dask version: 2021.01.1
Python version: 3.7.6
Operating System: MacOS
Install method (conda, pip, source): pip

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abduhbm linked a pull request

that will close this issue

Fix simple impute #788

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