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ENH Adds FeatureUnion.__getitem__ to access transformers #25093

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Merged
merged 5 commits into from
Dec 6, 2022
Merged

ENH Adds FeatureUnion.__getitem__ to access transformers #25093

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4471af0
ENH Adds FeatureUnion.__getitem__ to access transformers
thomasjpfan Dec 1, 2022
11ccc95
DOC Adds whats new number
thomasjpfan Dec 1, 2022
f5a5930
Update sklearn/tests/test_pipeline.py
thomasjpfan Dec 2, 2022
f77b492
Merge remote-tracking branch 'upstream/main' into feature_union_getitem
thomasjpfan Dec 5, 2022
07c55cc
ENH Validate string keys in __getitem__
thomasjpfan Dec 5, 2022
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6 changes: 6 additions & 0 deletions doc/whats_new/v1.3.rst
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Expand Up @@ -36,6 +36,12 @@ Changelog
:pr:`123456` by :user:`Joe Bloggs <joeongithub>`.
where 123456 is the *pull request* number, not the issue number.

:mod:`sklearn.pipeline`
.......................
- |Feature| :class:`pipeline.FeatureUnion` can now use indexing notation (e.g.
`feature_union["scalar"]`) to access transformers by name. :pr:`25093` by
`Thomas Fan`_.

Code and Documentation Contributors
-----------------------------------

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6 changes: 6 additions & 0 deletions sklearn/pipeline.py
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Expand Up @@ -1286,6 +1286,12 @@ def _sk_visual_block_(self):
names, transformers = zip(*self.transformer_list)
return _VisualBlock("parallel", transformers, names=names)

def __getitem__(self, name):
"""Return transformer with name."""
if not isinstance(name, str):
raise KeyError("Only string keys are supported")
return self.named_transformers[name]


def make_union(*transformers, n_jobs=None, verbose=False):
"""Construct a FeatureUnion from the given transformers.
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29 changes: 29 additions & 0 deletions sklearn/tests/test_pipeline.py
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Expand Up @@ -1658,3 +1658,32 @@ def test_feature_union_set_output():
assert isinstance(X_trans, pd.DataFrame)
assert_array_equal(X_trans.columns, union.get_feature_names_out())
assert_array_equal(X_trans.index, X_test.index)


def test_feature_union_getitem():
"""Check FeatureUnion.__getitem__ returns expected results."""
scalar = StandardScaler()
pca = PCA()
union = FeatureUnion(
[
("scalar", scalar),
("pca", pca),
("pass", "passthrough"),
("drop_me", "drop"),
]
)
assert union["scalar"] is scalar
assert union["pca"] is pca
assert union["pass"] == "passthrough"
assert union["drop_me"] == "drop"


@pytest.mark.parametrize("key", [0, slice(0, 2)])
def test_feature_union_getitem_error(key):
"""Raise error when __getitem__ gets a non-string input."""

union = FeatureUnion([("scalar", StandardScaler()), ("pca", PCA())])

msg = "Only string keys are supported"
with pytest.raises(KeyError, match=msg):
union[key]