* FIX Raise error on reordered columns in ColumnTransformer with remainder
* FIX Check for different length of X.columns to avoid exception
* FIX linter, line too long
* FIX import _check_key_type from its new location utils
* ENH Adjust doc, allow added columns
* Fix comment typo as suggested, remove non-essential exposition in doc
* Add PR 14237 to what's new
* Avoid AttributeError in favor of ValueError "column names only for DF"
* ENH Add check for n_features_ for array-likes and DataFrames
* Rename self.n_features to self._n_features
* Replaced backslash line continuation with parenthesis
* Style changes
* fix having mixed types in a single passthrough
* use check_array
* add comment
* Reference the relevant issue in the test
* don't force finite on check_array
* add the whats_new entry
* modify whats_new entry for a [probably] better description.
* raise a value error if columns can't be stacked.
* test the custom ValueError
* take sparse.hstack out of try/catch
* improve whats_new entry
* add comment for the dtype conversion
* change the tests to use an np of dtype 'O' instead
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Fixes#12096.
#### What does this implement/fix? Explain your changes.
Converts the input list for ColumnTransformer to a numpy array.
Added a check inside `transform` and `fit_transform` to check if the input `X` is a list, if it is then it gets converted to a numpy array.
#### Any other comments?
Should this conversion be documented in the docstrings for ColumnTransfomer's `fit`, `transform` and `fit_transform`?
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Reasoning: when eg OneHotEncoder is used as part of ColumnTransformer it would cause the final result to be a sparse matrix. As this is a typical case when we have mixed dtype data, it means that many pipeline will have to deal with sparse data implicitly, even if you have only some categorical features with low cardinality.
Idea was first to change default of `OneHotEncoder` sparse to False, but based on gitter discussion (https://gitter.im/scikit-learn/dev?at=5b4e5a69a94c5255523bc9fc) we decided to let ColumnTransformer switch between both based on a threshold. The user still has full control if he/she wants always or never sparse.
* define select_types callable factory
* include dtype column selector example
* support selector function for remainder=passthrough (already worked for drop)
* add docstring to example file. apparently sphinx fails if missing
* remove example and select_dtype factory
* generalize callable case (all specification types) + add tests
* add docstring
Thomas J. Fan
Hanmin Qin