[MRG] add drop_first option to OneHotEncoder #12884
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Note to reviewers: #12908 is more general so maybe review this one instead |
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Reference Issues/PRs
Closes #6488
What does this implement/fix? Explain your changes.
This PR adds a
drop_firstoption toOneHotEncoder.Each feature is encoded into
n_unique_values - 1columns instead ofn_unique_valuescolumns. The first one is dropped, resulting in all of the others being zero.Any other comments?
This is incompatible with
handle_missing='ignore'because the ignored missing categories result in all of the one-hot columns being zeros, which is also how the first category is treated whendrop_first=True. So by allowing both, there would be no way to distinguish between a missing category and the first one.