_column_transformer.py

"""
The :mod:`sklearn.compose._column_transformer` module implements utilities
to work with heterogeneous data and to apply different transformers to
different columns.
"""
# Author: Andreas Mueller
#         Joris Van den Bossche
# License: BSD
from numbers import Integral, Real
from itertools import chain
from collections import Counter

import numpy as np
from scipy import sparse

from ..base import clone, TransformerMixin
from ..utils._estimator_html_repr import _VisualBlock
from ..pipeline import _fit_transform_one, _transform_one, _name_estimators
from ..preprocessing import FunctionTransformer
from ..utils import Bunch
from ..utils import _safe_indexing
from ..utils import _get_column_indices
from ..utils._param_validation import HasMethods, Interval, StrOptions, Hidden
from ..utils._set_output import _get_output_config, _safe_set_output
from ..utils import check_pandas_support
from ..utils.metaestimators import _BaseComposition
from ..utils.validation import check_array, check_is_fitted, _check_feature_names_in
from ..utils.parallel import delayed, Parallel


__all__ = ["ColumnTransformer", "make_column_transformer", "make_column_selector"]


_ERR_MSG_1DCOLUMN = (
    "1D data passed to a transformer that expects 2D data. "
    "Try to specify the column selection as a list of one "
    "item instead of a scalar."
)


class ColumnTransformer(TransformerMixin, _BaseComposition):
    """Applies transformers to columns of an array or pandas DataFrame.

    This estimator allows different columns or column subsets of the input
    to be transformed separately and the features generated by each transformer
    will be concatenated to form a single feature space.
    This is useful for heterogeneous or columnar data, to combine several
    feature extraction mechanisms or transformations into a single transformer.

    Read more in the :ref:`User Guide <column_transformer>`.

    .. versionadded:: 0.20

    Parameters
    ----------
    transformers : list of tuples
        List of (name, transformer, columns) tuples specifying the
        transformer objects to be applied to subsets of the data.

        name : str
            Like in Pipeline and FeatureUnion, this allows the transformer and
            its parameters to be set using ``set_params`` and searched in grid
            search.
        transformer : {'drop', 'passthrough'} or estimator
            Estimator must support :term:`fit` and :term:`transform`.
            Special-cased strings 'drop' and 'passthrough' are accepted as
            well, to indicate to drop the columns or to pass them through
            untransformed, respectively.
        columns :  str, array-like of str, int, array-like of int, \
                array-like of bool, slice or callable
            Indexes the data on its second axis. Integers are interpreted as
            positional columns, while strings can reference DataFrame columns
            by name.  A scalar string or int should be used where
            ``transformer`` expects X to be a 1d array-like (vector),
            otherwise a 2d array will be passed to the transformer.
            A callable is passed the input data `X` and can return any of the
            above. To select multiple columns by name or dtype, you can use
            :obj:`make_column_selector`.

    remainder : {'drop', 'passthrough'} or estimator, default='drop'
        By default, only the specified columns in `transformers` are
        transformed and combined in the output, and the non-specified
        columns are dropped. (default of ``'drop'``).
        By specifying ``remainder='passthrough'``, all remaining columns that
        were not specified in `transformers`, but present in the data passed
        to `fit` will be automatically passed through. This subset of columns
        is concatenated with the output of the transformers. For dataframes,
        extra columns not seen during `fit` will be excluded from the output
        of `transform`.
        By setting ``remainder`` to be an estimator, the remaining
        non-specified columns will use the ``remainder`` estimator. The
        estimator must support :term:`fit` and :term:`transform`.
        Note that using this feature requires that the DataFrame columns
        input at :term:`fit` and :term:`transform` have identical order.

    sparse_threshold : float, default=0.3
        If the output of the different transformers contains sparse matrices,
        these will be stacked as a sparse matrix if the overall density is
        lower than this value. Use ``sparse_threshold=0`` to always return
        dense.  When the transformed output consists of all dense data, the
        stacked result will be dense, and this keyword will be ignored.

    n_jobs : int, default=None
        Number of jobs to run in parallel.
        ``None`` means 1 unless in a :obj:`joblib.parallel_backend` context.
        ``-1`` means using all processors. See :term:`Glossary <n_jobs>`
        for more details.

    transformer_weights : dict, default=None
        Multiplicative weights for features per transformer. The output of the
        transformer is multiplied by these weights. Keys are transformer names,
        values the weights.

    verbose : bool, default=False
        If True, the time elapsed while fitting each transformer will be
        printed as it is completed.

    verbose_feature_names_out : bool, default=True
        If True, :meth:`get_feature_names_out` will prefix all feature names
        with the name of the transformer that generated that feature.
        If False, :meth:`get_feature_names_out` will not prefix any feature
        names and will error if feature names are not unique.

        .. versionadded:: 1.0

    Attributes
    ----------
    transformers_ : list
        The collection of fitted transformers as tuples of
        (name, fitted_transformer, column). `fitted_transformer` can be an
        estimator, 'drop', or 'passthrough'. In case there were no columns
        selected, this will be the unfitted transformer.
        If there are remaining columns, the final element is a tuple of the
        form:
        ('remainder', transformer, remaining_columns) corresponding to the
        ``remainder`` parameter. If there are remaining columns, then
        ``len(transformers_)==len(transformers)+1``, otherwise
        ``len(transformers_)==len(transformers)``.

    named_transformers_ : :class:`~sklearn.utils.Bunch`
        Read-only attribute to access any transformer by given name.
        Keys are transformer names and values are the fitted transformer
        objects.

    sparse_output_ : bool
        Boolean flag indicating whether the output of ``transform`` is a
        sparse matrix or a dense numpy array, which depends on the output
        of the individual transformers and the `sparse_threshold` keyword.

    output_indices_ : dict
        A dictionary from each transformer name to a slice, where the slice
        corresponds to indices in the transformed output. This is useful to
        inspect which transformer is responsible for which transformed
        feature(s).

        .. versionadded:: 1.0

    n_features_in_ : int
        Number of features seen during :term:`fit`. Only defined if the
        underlying transformers expose such an attribute when fit.

        .. versionadded:: 0.24

    See Also
    --------
    make_column_transformer : Convenience function for
        combining the outputs of multiple transformer objects applied to
        column subsets of the original feature space.
    make_column_selector : Convenience function for selecting
        columns based on datatype or the columns name with a regex pattern.

    Notes
    -----
    The order of the columns in the transformed feature matrix follows the
    order of how the columns are specified in the `transformers` list.
    Columns of the original feature matrix that are not specified are
    dropped from the resulting transformed feature matrix, unless specified
    in the `passthrough` keyword. Those columns specified with `passthrough`
    are added at the right to the output of the transformers.

    Examples
    --------
    >>> import numpy as np
    >>> from sklearn.compose import ColumnTransformer
    >>> from sklearn.preprocessing import Normalizer
    >>> ct = ColumnTransformer(
    ...     [("norm1", Normalizer(norm='l1'), [0, 1]),
    ...      ("norm2", Normalizer(norm='l1'), slice(2, 4))])
    >>> X = np.array([[0., 1., 2., 2.],
    ...               [1., 1., 0., 1.]])
    >>> # Normalizer scales each row of X to unit norm. A separate scaling
    >>> # is applied for the two first and two last elements of each
    >>> # row independently.
    >>> ct.fit_transform(X)
    array([[0. , 1. , 0.5, 0.5],
           [0.5, 0.5, 0. , 1. ]])

    :class:`ColumnTransformer` can be configured with a transformer that requires
    a 1d array by setting the column to a string:

    >>> from sklearn.feature_extraction import FeatureHasher
    >>> from sklearn.preprocessing import MinMaxScaler
    >>> import pandas as pd   # doctest: +SKIP
    >>> X = pd.DataFrame({
    ...     "documents": ["First item", "second one here", "Is this the last?"],
    ...     "width": [3, 4, 5],
    ... })  # doctest: +SKIP
    >>> # "documents" is a string which configures ColumnTransformer to
    >>> # pass the documents column as a 1d array to the FeatureHasher
    >>> ct = ColumnTransformer(
    ...     [("text_preprocess", FeatureHasher(input_type="string"), "documents"),
    ...      ("num_preprocess", MinMaxScaler(), ["width"])])
    >>> X_trans = ct.fit_transform(X)  # doctest: +SKIP
    """

    _required_parameters = ["transformers"]

    _parameter_constraints: dict = {
        "transformers": [list, Hidden(tuple)],
        "remainder": [
            StrOptions({"drop", "passthrough"}),
            HasMethods(["fit", "transform"]),
            HasMethods(["fit_transform", "transform"]),
        ],
        "sparse_threshold": [Interval(Real, 0, 1, closed="both")],
        "n_jobs": [Integral, None],
        "transformer_weights": [dict, None],
        "verbose": ["verbose"],
        "verbose_feature_names_out": ["boolean"],
    }

    def __init__(
        self,
        transformers,
        *,
        remainder="drop",
        sparse_threshold=0.3,
        n_jobs=None,
        transformer_weights=None,
        verbose=False,
        verbose_feature_names_out=True,
    ):
        self.transformers = transformers
        self.remainder = remainder
        self.sparse_threshold = sparse_threshold
        self.n_jobs = n_jobs
        self.transformer_weights = transformer_weights
        self.verbose = verbose
        self.verbose_feature_names_out = verbose_feature_names_out

    @property
    def _transformers(self):
        """
        Internal list of transformer only containing the name and
        transformers, dropping the columns. This is for the implementation
        of get_params via BaseComposition._get_params which expects lists
        of tuples of len 2.
        """
        try:
            return [(name, trans) for name, trans, _ in self.transformers]
        except (TypeError, ValueError):
            return self.transformers

    @_transformers.setter
    def _transformers(self, value):
        try:
            self.transformers = [
                (name, trans, col)
                for ((name, trans), (_, _, col)) in zip(value, self.transformers)
            ]
        except (TypeError, ValueError):
            self.transformers = value

    def set_output(self, *, transform=None):
        """Set the output container when `"transform"` and `"fit_transform"` are called.

        Calling `set_output` will set the output of all estimators in `transformers`
        and `transformers_`.

        Parameters
        ----------
        transform : {"default", "pandas"}, default=None
            Configure output of `transform` and `fit_transform`.

            - `"default"`: Default output format of a transformer
            - `"pandas"`: DataFrame output
            - `None`: Transform configuration is unchanged

        Returns
        -------
        self : estimator instance
            Estimator instance.
        """
        super().set_output(transform=transform)
        transformers = (
            trans
            for _, trans, _ in chain(
                self.transformers, getattr(self, "transformers_", [])
            )
            if trans not in {"passthrough", "drop"}
        )
        for trans in transformers:
            _safe_set_output(trans, transform=transform)

        return self

    def get_params(self, deep=True):
        """Get parameters for this estimator.

        Returns the parameters given in the constructor as well as the
        estimators contained within the `transformers` of the
        `ColumnTransformer`.

        Parameters
        ----------
        deep : bool, default=True
            If True, will return the parameters for this estimator and
            contained subobjects that are estimators.

        Returns
        -------
        params : dict
            Parameter names mapped to their values.
        """
        return self._get_params("_transformers", deep=deep)

    def set_params(self, **kwargs):
        """Set the parameters of this estimator.

        Valid parameter keys can be listed with ``get_params()``. Note that you
        can directly set the parameters of the estimators contained in
        `transformers` of `ColumnTransformer`.

        Parameters
        ----------
        **kwargs : dict
            Estimator parameters.

        Returns
        -------
        self : ColumnTransformer
            This estimator.
        """
        self._set_params("_transformers", **kwargs)
        return self

    def _iter(self, fitted=False, replace_strings=False, column_as_strings=False):
        """
        Generate (name, trans, column, weight) tuples.

        If fitted=True, use the fitted transformers, else use the
        user specified transformers updated with converted column names
        and potentially appended with transformer for remainder.

        """
        if fitted:
            if replace_strings:
                # Replace "passthrough" with the fitted version in
                # _name_to_fitted_passthrough
                def replace_passthrough(name, trans, columns):
                    if name not in self._name_to_fitted_passthrough:
                        return name, trans, columns
                    return name, self._name_to_fitted_passthrough[name], columns

                transformers = [
                    replace_passthrough(*trans) for trans in self.transformers_
                ]
            else:
                transformers = self.transformers_
        else:
            # interleave the validated column specifiers
            transformers = [
                (name, trans, column)
                for (name, trans, _), column in zip(self.transformers, self._columns)
            ]
            # add transformer tuple for remainder
            if self._remainder[2]:
                transformers = chain(transformers, [self._remainder])
        get_weight = (self.transformer_weights or {}).get

        output_config = _get_output_config("transform", self)
        for name, trans, columns in transformers:
            if replace_strings:
                # replace 'passthrough' with identity transformer and
                # skip in case of 'drop'
                if trans == "passthrough":
                    trans = FunctionTransformer(
                        accept_sparse=True,
                        check_inverse=False,
                        feature_names_out="one-to-one",
                    ).set_output(transform=output_config["dense"])
                elif trans == "drop":
                    continue
                elif _is_empty_column_selection(columns):
                    continue

            if column_as_strings:
                # Convert all columns to using their string labels
                columns_is_scalar = np.isscalar(columns)

                indices = self._transformer_to_input_indices[name]
                columns = self.feature_names_in_[indices]

                if columns_is_scalar:
                    # selection is done with one dimension
                    columns = columns[0]

            yield (name, trans, columns, get_weight(name))

    def _validate_transformers(self):
        if not self.transformers:
            return

        names, transformers, _ = zip(*self.transformers)

        # validate names
        self._validate_names(names)

        # validate estimators
        for t in transformers:
            if t in ("drop", "passthrough"):
                continue
            if not (hasattr(t, "fit") or hasattr(t, "fit_transform")) or not hasattr(
                t, "transform"
            ):
                # Used to validate the transformers in the `transformers` list
                raise TypeError(
                    "All estimators should implement fit and "
                    "transform, or can be 'drop' or 'passthrough' "
                    "specifiers. '%s' (type %s) doesn't." % (t, type(t))
                )

    def _validate_column_callables(self, X):
        """
        Converts callable column specifications.
        """
        all_columns = []
        transformer_to_input_indices = {}
        for name, _, columns in self.transformers:
            if callable(columns):
                columns = columns(X)
            all_columns.append(columns)
            transformer_to_input_indices[name] = _get_column_indices(X, columns)

        self._columns = all_columns
        self._transformer_to_input_indices = transformer_to_input_indices

    def _validate_remainder(self, X):
        """
        Validates ``remainder`` and defines ``_remainder`` targeting
        the remaining columns.
        """
        self._n_features = X.shape[1]
        cols = set(chain(*self._transformer_to_input_indices.values()))
        remaining = sorted(set(range(self._n_features)) - cols)
        self._remainder = ("remainder", self.remainder, remaining)
        self._transformer_to_input_indices["remainder"] = remaining

    @property
    def named_transformers_(self):
        """Access the fitted transformer by name.

        Read-only attribute to access any transformer by given name.
        Keys are transformer names and values are the fitted transformer
        objects.
        """
        # Use Bunch object to improve autocomplete
        return Bunch(**{name: trans for name, trans, _ in self.transformers_})

    def _get_feature_name_out_for_transformer(
        self, name, trans, column, feature_names_in
    ):
        """Gets feature names of transformer.

        Used in conjunction with self._iter(fitted=True) in get_feature_names_out.
        """
        column_indices = self._transformer_to_input_indices[name]
        names = feature_names_in[column_indices]
        if trans == "drop" or _is_empty_column_selection(column):
            return
        elif trans == "passthrough":
            return names

        # An actual transformer
        if not hasattr(trans, "get_feature_names_out"):
            raise AttributeError(
                f"Transformer {name} (type {type(trans).__name__}) does "
                "not provide get_feature_names_out."
            )
        return trans.get_feature_names_out(names)

    def get_feature_names_out(self, input_features=None):
        """Get output feature names for transformation.

        Parameters
        ----------
        input_features : array-like of str or None, default=None
            Input features.

            - If `input_features` is `None`, then `feature_names_in_` is
              used as feature names in. If `feature_names_in_` is not defined,
              then the following input feature names are generated:
              `["x0", "x1", ..., "x(n_features_in_ - 1)"]`.
            - If `input_features` is an array-like, then `input_features` must
              match `feature_names_in_` if `feature_names_in_` is defined.

        Returns
        -------
        feature_names_out : ndarray of str objects
            Transformed feature names.
        """
        check_is_fitted(self)
        input_features = _check_feature_names_in(self, input_features)

        # List of tuples (name, feature_names_out)
        transformer_with_feature_names_out = []
        for name, trans, column, _ in self._iter(fitted=True):
            feature_names_out = self._get_feature_name_out_for_transformer(
                name, trans, column, input_features
            )
            if feature_names_out is None:
                continue
            transformer_with_feature_names_out.append((name, feature_names_out))

        if not transformer_with_feature_names_out:
            # No feature names
            return np.array([], dtype=object)

        return self._add_prefix_for_feature_names_out(
            transformer_with_feature_names_out
        )

    def _add_prefix_for_feature_names_out(self, transformer_with_feature_names_out):
        """Add prefix for feature names out that includes the transformer names.

        Parameters
        ----------
        transformer_with_feature_names_out : list of tuples of (str, array-like of str)
            The tuple consistent of the transformer's name and its feature names out.

        Returns
        -------
        feature_names_out : ndarray of shape (n_features,), dtype=str
            Transformed feature names.
        """
        if self.verbose_feature_names_out:
            # Prefix the feature names out with the transformers name
            names = list(
                chain.from_iterable(
                    (f"{name}__{i}" for i in feature_names_out)
                    for name, feature_names_out in transformer_with_feature_names_out
                )
            )
            return np.asarray(names, dtype=object)

        # verbose_feature_names_out is False
        # Check that names are all unique without a prefix
        feature_names_count = Counter(
            chain.from_iterable(s for _, s in transformer_with_feature_names_out)
        )
        top_6_overlap = [
            name for name, count in feature_names_count.most_common(6) if count > 1
        ]
        top_6_overlap.sort()
        if top_6_overlap:
            if len(top_6_overlap) == 6:
                # There are more than 5 overlapping names, we only show the 5
                # of the feature names
                names_repr = str(top_6_overlap[:5])[:-1] + ", ...]"
            else:
                names_repr = str(top_6_overlap)
            raise ValueError(
                f"Output feature names: {names_repr} are not unique. Please set "
                "verbose_feature_names_out=True to add prefixes to feature names"
            )

        return np.concatenate(
            [name for _, name in transformer_with_feature_names_out],
        )

    def _update_fitted_transformers(self, transformers):
        # transformers are fitted; excludes 'drop' cases
        fitted_transformers = iter(transformers)
        transformers_ = []
        self._name_to_fitted_passthrough = {}

        for name, old, column, _ in self._iter():
            if old == "drop":
                trans = "drop"
            elif old == "passthrough":
                # FunctionTransformer is present in list of transformers,
                # so get next transformer, but save original string
                func_transformer = next(fitted_transformers)
                trans = "passthrough"

                # The fitted FunctionTransformer is saved in another attribute,
                # so it can be used during transform for set_output.
                self._name_to_fitted_passthrough[name] = func_transformer
            elif _is_empty_column_selection(column):
                trans = old
            else:
                trans = next(fitted_transformers)
            transformers_.append((name, trans, column))

        # sanity check that transformers is exhausted
        assert not list(fitted_transformers)
        self.transformers_ = transformers_

    def _validate_output(self, result):
        """
        Ensure that the output of each transformer is 2D. Otherwise
        hstack can raise an error or produce incorrect results.
        """
        names = [
            name for name, _, _, _ in self._iter(fitted=True, replace_strings=True)
        ]
        for Xs, name in zip(result, names):
            if not getattr(Xs, "ndim", 0) == 2:
                raise ValueError(
                    "The output of the '{0}' transformer should be 2D (scipy "
                    "matrix, array, or pandas DataFrame).".format(name)
                )

    def _record_output_indices(self, Xs):
        """
        Record which transformer produced which column.
        """
        idx = 0
        self.output_indices_ = {}

        for transformer_idx, (name, _, _, _) in enumerate(
            self._iter(fitted=True, replace_strings=True)
        ):
            n_columns = Xs[transformer_idx].shape[1]
            self.output_indices_[name] = slice(idx, idx + n_columns)
            idx += n_columns

        # `_iter` only generates transformers that have a non empty
        # selection. Here we set empty slices for transformers that
        # generate no output, which are safe for indexing
        all_names = [t[0] for t in self.transformers] + ["remainder"]
        for name in all_names:
            if name not in self.output_indices_:
                self.output_indices_[name] = slice(0, 0)

    def _log_message(self, name, idx, total):
        if not self.verbose:
            return None
        return "(%d of %d) Processing %s" % (idx, total, name)

    def _fit_transform(self, X, y, func, fitted=False, column_as_strings=False):
        """
        Private function to fit and/or transform on demand.

        Return value (transformers and/or transformed X data) depends
        on the passed function.
        ``fitted=True`` ensures the fitted transformers are used.
        """
        transformers = list(
            self._iter(
                fitted=fitted, replace_strings=True, column_as_strings=column_as_strings
            )
        )
        try:
            return Parallel(n_jobs=self.n_jobs)(
                delayed(func)(
                    transformer=clone(trans) if not fitted else trans,
                    X=_safe_indexing(X, column, axis=1),
                    y=y,
                    weight=weight,
                    message_clsname="ColumnTransformer",
                    message=self._log_message(name, idx, len(transformers)),
                )
                for idx, (name, trans, column, weight) in enumerate(transformers, 1)
            )
        except ValueError as e:
            if "Expected 2D array, got 1D array instead" in str(e):
                raise ValueError(_ERR_MSG_1DCOLUMN) from e
            else:
                raise

    def fit(self, X, y=None):
        """Fit all transformers using X.

        Parameters
        ----------
        X : {array-like, dataframe} of shape (n_samples, n_features)
            Input data, of which specified subsets are used to fit the
            transformers.

        y : array-like of shape (n_samples,...), default=None
            Targets for supervised learning.

        Returns
        -------
        self : ColumnTransformer
            This estimator.
        """
        self._validate_params()
        # we use fit_transform to make sure to set sparse_output_ (for which we
        # need the transformed data) to have consistent output type in predict
        self.fit_transform(X, y=y)
        return self

    def fit_transform(self, X, y=None):
        """Fit all transformers, transform the data and concatenate results.

        Parameters
        ----------
        X : {array-like, dataframe} of shape (n_samples, n_features)
            Input data, of which specified subsets are used to fit the
            transformers.

        y : array-like of shape (n_samples,), default=None
            Targets for supervised learning.

        Returns
        -------
        X_t : {array-like, sparse matrix} of \
                shape (n_samples, sum_n_components)
            Horizontally stacked results of transformers. sum_n_components is the
            sum of n_components (output dimension) over transformers. If
            any result is a sparse matrix, everything will be converted to
            sparse matrices.
        """
        self._validate_params()
        self._check_feature_names(X, reset=True)

        X = _check_X(X)
        # set n_features_in_ attribute
        self._check_n_features(X, reset=True)
        self._validate_transformers()
        self._validate_column_callables(X)
        self._validate_remainder(X)

        result = self._fit_transform(X, y, _fit_transform_one)

        if not result:
            self._update_fitted_transformers([])
            # All transformers are None
            return np.zeros((X.shape[0], 0))

        Xs, transformers = zip(*result)

        # determine if concatenated output will be sparse or not
        if any(sparse.issparse(X) for X in Xs):
            nnz = sum(X.nnz if sparse.issparse(X) else X.size for X in Xs)
            total = sum(
                X.shape[0] * X.shape[1] if sparse.issparse(X) else X.size for X in Xs
            )
            density = nnz / total
            self.sparse_output_ = density < self.sparse_threshold
        else:
            self.sparse_output_ = False

        self._update_fitted_transformers(transformers)
        self._validate_output(Xs)
        self._record_output_indices(Xs)

        return self._hstack(list(Xs))

    def transform(self, X):
        """Transform X separately by each transformer, concatenate results.

        Parameters
        ----------
        X : {array-like, dataframe} of shape (n_samples, n_features)
            The data to be transformed by subset.

        Returns
        -------
        X_t : {array-like, sparse matrix} of \
                shape (n_samples, sum_n_components)
            Horizontally stacked results of transformers. sum_n_components is the
            sum of n_components (output dimension) over transformers. If
            any result is a sparse matrix, everything will be converted to
            sparse matrices.
        """
        check_is_fitted(self)
        X = _check_X(X)

        fit_dataframe_and_transform_dataframe = hasattr(
            self, "feature_names_in_"
        ) and hasattr(X, "columns")

        if fit_dataframe_and_transform_dataframe:
            named_transformers = self.named_transformers_
            # check that all names seen in fit are in transform, unless
            # they were dropped
            non_dropped_indices = [
                ind
                for name, ind in self._transformer_to_input_indices.items()
                if name in named_transformers
                and isinstance(named_transformers[name], str)
                and named_transformers[name] != "drop"
            ]

            all_indices = set(chain(*non_dropped_indices))
            all_names = set(self.feature_names_in_[ind] for ind in all_indices)

            diff = all_names - set(X.columns)
            if diff:
                raise ValueError(f"columns are missing: {diff}")
        else:
            # ndarray was used for fitting or transforming, thus we only
            # check that n_features_in_ is consistent
            self._check_n_features(X, reset=False)

        Xs = self._fit_transform(
            X,
            None,
            _transform_one,
            fitted=True,
            column_as_strings=fit_dataframe_and_transform_dataframe,
        )
        self._validate_output(Xs)

        if not Xs:
            # All transformers are None
            return np.zeros((X.shape[0], 0))

        return self._hstack(list(Xs))

    def _hstack(self, Xs):
        """Stacks Xs horizontally.

        This allows subclasses to control the stacking behavior, while reusing
        everything else from ColumnTransformer.

        Parameters
        ----------
        Xs : list of {array-like, sparse matrix, dataframe}
        """
        if self.sparse_output_:
            try:
                # since all columns should be numeric before stacking them
                # in a sparse matrix, `check_array` is used for the
                # dtype conversion if necessary.
                converted_Xs = [
                    check_array(X, accept_sparse=True, force_all_finite=False)
                    for X in Xs
                ]
            except ValueError as e:
                raise ValueError(
                    "For a sparse output, all columns should "
                    "be a numeric or convertible to a numeric."
                ) from e

            return sparse.hstack(converted_Xs).tocsr()
        else:
            Xs = [f.toarray() if sparse.issparse(f) else f for f in Xs]
            config = _get_output_config("transform", self)
            if config["dense"] == "pandas" and all(hasattr(X, "iloc") for X in Xs):
                pd = check_pandas_support("transform")
                output = pd.concat(Xs, axis=1)

                # If all transformers define `get_feature_names_out`, then transform
                # will adjust the column names to be consistent with
                # verbose_feature_names_out. Here we prefix the feature names if
                # verbose_feature_names_out=True.

                if not self.verbose_feature_names_out:
                    return output

                transformer_names = [
                    t[0] for t in self._iter(fitted=True, replace_strings=True)
                ]
                feature_names_outs = [X.columns for X in Xs]
                names_out = self._add_prefix_for_feature_names_out(
                    list(zip(transformer_names, feature_names_outs))
                )
                output.columns = names_out
                return output

            return np.hstack(Xs)

    def _sk_visual_block_(self):
        if isinstance(self.remainder, str) and self.remainder == "drop":
            transformers = self.transformers
        elif hasattr(self, "_remainder"):
            remainder_columns = self._remainder[2]
            if (
                hasattr(self, "feature_names_in_")
                and remainder_columns
                and not all(isinstance(col, str) for col in remainder_columns)
            ):
                remainder_columns = self.feature_names_in_[remainder_columns].tolist()
            transformers = chain(
                self.transformers, [("remainder", self.remainder, remainder_columns)]
            )
        else:
            transformers = chain(self.transformers, [("remainder", self.remainder, "")])

        names, transformers, name_details = zip(*transformers)
        return _VisualBlock(
            "parallel", transformers, names=names, name_details=name_details
        )


def _check_X(X):
    """Use check_array only on lists and other non-array-likes / sparse"""
    if hasattr(X, "__array__") or sparse.issparse(X):
        return X
    return check_array(X, force_all_finite="allow-nan", dtype=object)


def _is_empty_column_selection(column):
    """
    Return True if the column selection is empty (empty list or all-False
    boolean array).

    """
    if hasattr(column, "dtype") and np.issubdtype(column.dtype, np.bool_):
        return not column.any()
    elif hasattr(column, "__len__"):
        return (
            len(column) == 0
            or all(isinstance(col, bool) for col in column)
            and not any(column)
        )
    else:
        return False


def _get_transformer_list(estimators):
    """
    Construct (name, trans, column) tuples from list

    """
    transformers, columns = zip(*estimators)
    names, _ = zip(*_name_estimators(transformers))

    transformer_list = list(zip(names, transformers, columns))
    return transformer_list


def make_column_transformer(
    *transformers,
    remainder="drop",
    sparse_threshold=0.3,
    n_jobs=None,
    verbose=False,
    verbose_feature_names_out=True,
):
    """Construct a ColumnTransformer from the given transformers.

    This is a shorthand for the ColumnTransformer constructor; it does not
    require, and does not permit, naming the transformers. Instead, they will
    be given names automatically based on their types. It also does not allow
    weighting with ``transformer_weights``.

    Read more in the :ref:`User Guide <make_column_transformer>`.

    Parameters
    ----------
    *transformers : tuples
        Tuples of the form (transformer, columns) specifying the
        transformer objects to be applied to subsets of the data.

        transformer : {'drop', 'passthrough'} or estimator
            Estimator must support :term:`fit` and :term:`transform`.
            Special-cased strings 'drop' and 'passthrough' are accepted as
            well, to indicate to drop the columns or to pass them through
            untransformed, respectively.
        columns : str,  array-like of str, int, array-like of int, slice, \
                array-like of bool or callable
            Indexes the data on its second axis. Integers are interpreted as
            positional columns, while strings can reference DataFrame columns
            by name. A scalar string or int should be used where
            ``transformer`` expects X to be a 1d array-like (vector),
            otherwise a 2d array will be passed to the transformer.
            A callable is passed the input data `X` and can return any of the
            above. To select multiple columns by name or dtype, you can use
            :obj:`make_column_selector`.

    remainder : {'drop', 'passthrough'} or estimator, default='drop'
        By default, only the specified columns in `transformers` are
        transformed and combined in the output, and the non-specified
        columns are dropped. (default of ``'drop'``).
        By specifying ``remainder='passthrough'``, all remaining columns that
        were not specified in `transformers` will be automatically passed
        through. This subset of columns is concatenated with the output of
        the transformers.
        By setting ``remainder`` to be an estimator, the remaining
        non-specified columns will use the ``remainder`` estimator. The
        estimator must support :term:`fit` and :term:`transform`.

    sparse_threshold : float, default=0.3
        If the transformed output consists of a mix of sparse and dense data,
        it will be stacked as a sparse matrix if the density is lower than this
        value. Use ``sparse_threshold=0`` to always return dense.
        When the transformed output consists of all sparse or all dense data,
        the stacked result will be sparse or dense, respectively, and this
        keyword will be ignored.

    n_jobs : int, default=None
        Number of jobs to run in parallel.
        ``None`` means 1 unless in a :obj:`joblib.parallel_backend` context.
        ``-1`` means using all processors. See :term:`Glossary <n_jobs>`
        for more details.

    verbose : bool, default=False
        If True, the time elapsed while fitting each transformer will be
        printed as it is completed.

    verbose_feature_names_out : bool, default=True
        If True, :meth:`get_feature_names_out` will prefix all feature names
        with the name of the transformer that generated that feature.
        If False, :meth:`get_feature_names_out` will not prefix any feature
        names and will error if feature names are not unique.

        .. versionadded:: 1.0

    Returns
    -------
    ct : ColumnTransformer
        Returns a :class:`ColumnTransformer` object.

    See Also
    --------
    ColumnTransformer : Class that allows combining the
        outputs of multiple transformer objects used on column subsets
        of the data into a single feature space.

    Examples
    --------
    >>> from sklearn.preprocessing import StandardScaler, OneHotEncoder
    >>> from sklearn.compose import make_column_transformer
    >>> make_column_transformer(
    ...     (StandardScaler(), ['numerical_column']),
    ...     (OneHotEncoder(), ['categorical_column']))
    ColumnTransformer(transformers=[('standardscaler', StandardScaler(...),
                                     ['numerical_column']),
                                    ('onehotencoder', OneHotEncoder(...),
                                     ['categorical_column'])])
    """
    # transformer_weights keyword is not passed through because the user
    # would need to know the automatically generated names of the transformers
    transformer_list = _get_transformer_list(transformers)
    return ColumnTransformer(
        transformer_list,
        n_jobs=n_jobs,
        remainder=remainder,
        sparse_threshold=sparse_threshold,
        verbose=verbose,
        verbose_feature_names_out=verbose_feature_names_out,
    )


class make_column_selector:
    """Create a callable to select columns to be used with
    :class:`ColumnTransformer`.

    :func:`make_column_selector` can select columns based on datatype or the
    columns name with a regex. When using multiple selection criteria, **all**
    criteria must match for a column to be selected.

    Parameters
    ----------
    pattern : str, default=None
        Name of columns containing this regex pattern will be included. If
        None, column selection will not be selected based on pattern.

    dtype_include : column dtype or list of column dtypes, default=None
        A selection of dtypes to include. For more details, see
        :meth:`pandas.DataFrame.select_dtypes`.

    dtype_exclude : column dtype or list of column dtypes, default=None
        A selection of dtypes to exclude. For more details, see
        :meth:`pandas.DataFrame.select_dtypes`.

    Returns
    -------
    selector : callable
        Callable for column selection to be used by a
        :class:`ColumnTransformer`.

    See Also
    --------
    ColumnTransformer : Class that allows combining the
        outputs of multiple transformer objects used on column subsets
        of the data into a single feature space.

    Examples
    --------
    >>> from sklearn.preprocessing import StandardScaler, OneHotEncoder
    >>> from sklearn.compose import make_column_transformer
    >>> from sklearn.compose import make_column_selector
    >>> import numpy as np
    >>> import pandas as pd  # doctest: +SKIP
    >>> X = pd.DataFrame({'city': ['London', 'London', 'Paris', 'Sallisaw'],
    ...                   'rating': [5, 3, 4, 5]})  # doctest: +SKIP
    >>> ct = make_column_transformer(
    ...       (StandardScaler(),
    ...        make_column_selector(dtype_include=np.number)),  # rating
    ...       (OneHotEncoder(),
    ...        make_column_selector(dtype_include=object)))  # city
    >>> ct.fit_transform(X)  # doctest: +SKIP
    array([[ 0.90453403,  1.        ,  0.        ,  0.        ],
           [-1.50755672,  1.        ,  0.        ,  0.        ],
           [-0.30151134,  0.        ,  1.        ,  0.        ],
           [ 0.90453403,  0.        ,  0.        ,  1.        ]])
    """

    def __init__(self, pattern=None, *, dtype_include=None, dtype_exclude=None):
        self.pattern = pattern
        self.dtype_include = dtype_include
        self.dtype_exclude = dtype_exclude

    def __call__(self, df):
        """Callable for column selection to be used by a
        :class:`ColumnTransformer`.

        Parameters
        ----------
        df : dataframe of shape (n_features, n_samples)
            DataFrame to select columns from.
        """
        if not hasattr(df, "iloc"):
            raise ValueError(
                "make_column_selector can only be applied to pandas dataframes"
            )
        df_row = df.iloc[:1]
        if self.dtype_include is not None or self.dtype_exclude is not None:
            df_row = df_row.select_dtypes(
                include=self.dtype_include, exclude=self.dtype_exclude
            )
        cols = df_row.columns
        if self.pattern is not None:
            cols = cols[cols.str.contains(self.pattern, regex=True)]
        return cols.tolist()