# Authors: Andreas Mueller # Joris Van den Bossche # License: BSD 3 clause import numpy as np from scipy import sparse from ..base import BaseEstimator, TransformerMixin from ..utils import check_array from ..utils.validation import check_is_fitted from ..utils.validation import _deprecate_positional_args from ._label import _encode, _encode_check_unknown __all__ = [ 'OneHotEncoder', 'OrdinalEncoder' ] class _BaseEncoder(TransformerMixin, BaseEstimator): """ Base class for encoders that includes the code to categorize and transform the input features. """ def _check_X(self, X): """ Perform custom check_array: - convert list of strings to object dtype - check for missing values for object dtype data (check_array does not do that) - return list of features (arrays): this list of features is constructed feature by feature to preserve the data types of pandas DataFrame columns, as otherwise information is lost and cannot be used, eg for the `categories_` attribute. """ if not (hasattr(X, 'iloc') and getattr(X, 'ndim', 0) == 2): # if not a dataframe, do normal check_array validation X_temp = check_array(X, dtype=None) if (not hasattr(X, 'dtype') and np.issubdtype(X_temp.dtype, np.str_)): X = check_array(X, dtype=np.object) else: X = X_temp needs_validation = False else: # pandas dataframe, do validation later column by column, in order # to keep the dtype information to be used in the encoder. needs_validation = True n_samples, n_features = X.shape X_columns = [] for i in range(n_features): Xi = self._get_feature(X, feature_idx=i) Xi = check_array(Xi, ensure_2d=False, dtype=None, force_all_finite=needs_validation) X_columns.append(Xi) return X_columns, n_samples, n_features def _get_feature(self, X, feature_idx): if hasattr(X, 'iloc'): # pandas dataframes return X.iloc[:, feature_idx] # numpy arrays, sparse arrays return X[:, feature_idx] def _fit(self, X, handle_unknown='error'): X_list, n_samples, n_features = self._check_X(X) if self.categories != 'auto': if len(self.categories) != n_features: raise ValueError("Shape mismatch: if categories is an array," " it has to be of shape (n_features,).") self.categories_ = [] for i in range(n_features): Xi = X_list[i] if self.categories == 'auto': cats = _encode(Xi) else: cats = np.array(self.categories[i], dtype=Xi.dtype) if Xi.dtype != object: if not np.all(np.sort(cats) == cats): raise ValueError("Unsorted categories are not " "supported for numerical categories") if handle_unknown == 'error': diff = _encode_check_unknown(Xi, cats) if diff: msg = ("Found unknown categories {0} in column {1}" " during fit".format(diff, i)) raise ValueError(msg) self.categories_.append(cats) def _transform(self, X, handle_unknown='error'): X_list, n_samples, n_features = self._check_X(X) X_int = np.zeros((n_samples, n_features), dtype=np.int) X_mask = np.ones((n_samples, n_features), dtype=np.bool) if n_features != len(self.categories_): raise ValueError( "The number of features in X is different to the number of " "features of the fitted data. The fitted data had {} features " "and the X has {} features." .format(len(self.categories_,), n_features) ) for i in range(n_features): Xi = X_list[i] diff, valid_mask = _encode_check_unknown(Xi, self.categories_[i], return_mask=True) if not np.all(valid_mask): if handle_unknown == 'error': msg = ("Found unknown categories {0} in column {1}" " during transform".format(diff, i)) raise ValueError(msg) else: # Set the problematic rows to an acceptable value and # continue `The rows are marked `X_mask` and will be # removed later. X_mask[:, i] = valid_mask # cast Xi into the largest string type necessary # to handle different lengths of numpy strings if (self.categories_[i].dtype.kind in ('U', 'S') and self.categories_[i].itemsize > Xi.itemsize): Xi = Xi.astype(self.categories_[i].dtype) else: Xi = Xi.copy() Xi[~valid_mask] = self.categories_[i][0] # We use check_unknown=False, since _encode_check_unknown was # already called above. _, encoded = _encode(Xi, self.categories_[i], encode=True, check_unknown=False) X_int[:, i] = encoded return X_int, X_mask def _more_tags(self): return {'X_types': ['categorical']} class OneHotEncoder(_BaseEncoder): """ Encode categorical features as a one-hot numeric array. The input to this transformer should be an array-like of integers or strings, denoting the values taken on by categorical (discrete) features. The features are encoded using a one-hot (aka 'one-of-K' or 'dummy') encoding scheme. This creates a binary column for each category and returns a sparse matrix or dense array (depending on the ``sparse`` parameter) By default, the encoder derives the categories based on the unique values in each feature. Alternatively, you can also specify the `categories` manually. This encoding is needed for feeding categorical data to many scikit-learn estimators, notably linear models and SVMs with the standard kernels. Note: a one-hot encoding of y labels should use a LabelBinarizer instead. Read more in the :ref:`User Guide `. .. versionchanged:: 0.20 Parameters ---------- categories : 'auto' or a list of array-like, default='auto' Categories (unique values) per feature: - 'auto' : Determine categories automatically from the training data. - list : ``categories[i]`` holds the categories expected in the ith column. The passed categories should not mix strings and numeric values within a single feature, and should be sorted in case of numeric values. The used categories can be found in the ``categories_`` attribute. .. versionadded:: 0.20 drop : {'first', 'if_binary'} or a array-like of shape (n_features,), \ default=None Specifies a methodology to use to drop one of the categories per feature. This is useful in situations where perfectly collinear features cause problems, such as when feeding the resulting data into a neural network or an unregularized regression. However, dropping one category breaks the symmetry of the original representation and can therefore induce a bias in downstream models, for instance for penalized linear classification or regression models. - None : retain all features (the default). - 'first' : drop the first category in each feature. If only one category is present, the feature will be dropped entirely. - 'if_binary' : drop the first category in each feature with two categories. Features with 1 or more than 2 categories are left intact. - array : ``drop[i]`` is the category in feature ``X[:, i]`` that should be dropped. sparse : bool, default=True Will return sparse matrix if set True else will return an array. dtype : number type, default=np.float Desired dtype of output. handle_unknown : {'error', 'ignore'}, default='error' Whether to raise an error or ignore if an unknown categorical feature is present during transform (default is to raise). When this parameter is set to 'ignore' and an unknown category is encountered during transform, the resulting one-hot encoded columns for this feature will be all zeros. In the inverse transform, an unknown category will be denoted as None. Attributes ---------- categories_ : list of arrays The categories of each feature determined during fitting (in order of the features in X and corresponding with the output of ``transform``). This includes the category specified in ``drop`` (if any). drop_idx_ : array of shape (n_features,) - ``drop_idx_[i]`` is the index in ``categories_[i]`` of the category to be dropped for each feature. - ``drop_idx_[i] = None`` if no category is to be dropped from the feature with index ``i``, e.g. when `drop='if_binary'` and the feature isn't binary. - ``drop_idx_ = None`` if all the transformed features will be retained. See Also -------- sklearn.preprocessing.OrdinalEncoder : Performs an ordinal (integer) encoding of the categorical features. sklearn.feature_extraction.DictVectorizer : Performs a one-hot encoding of dictionary items (also handles string-valued features). sklearn.feature_extraction.FeatureHasher : Performs an approximate one-hot encoding of dictionary items or strings. sklearn.preprocessing.LabelBinarizer : Binarizes labels in a one-vs-all fashion. sklearn.preprocessing.MultiLabelBinarizer : Transforms between iterable of iterables and a multilabel format, e.g. a (samples x classes) binary matrix indicating the presence of a class label. Examples -------- Given a dataset with two features, we let the encoder find the unique values per feature and transform the data to a binary one-hot encoding. >>> from sklearn.preprocessing import OneHotEncoder One can discard categories not seen during `fit`: >>> enc = OneHotEncoder(handle_unknown='ignore') >>> X = [['Male', 1], ['Female', 3], ['Female', 2]] >>> enc.fit(X) OneHotEncoder(handle_unknown='ignore') >>> enc.categories_ [array(['Female', 'Male'], dtype=object), array([1, 2, 3], dtype=object)] >>> enc.transform([['Female', 1], ['Male', 4]]).toarray() array([[1., 0., 1., 0., 0.], [0., 1., 0., 0., 0.]]) >>> enc.inverse_transform([[0, 1, 1, 0, 0], [0, 0, 0, 1, 0]]) array([['Male', 1], [None, 2]], dtype=object) >>> enc.get_feature_names(['gender', 'group']) array(['gender_Female', 'gender_Male', 'group_1', 'group_2', 'group_3'], dtype=object) One can always drop the first column for each feature: >>> drop_enc = OneHotEncoder(drop='first').fit(X) >>> drop_enc.categories_ [array(['Female', 'Male'], dtype=object), array([1, 2, 3], dtype=object)] >>> drop_enc.transform([['Female', 1], ['Male', 2]]).toarray() array([[0., 0., 0.], [1., 1., 0.]]) Or drop a column for feature only having 2 categories: >>> drop_binary_enc = OneHotEncoder(drop='if_binary').fit(X) >>> drop_binary_enc.transform([['Female', 1], ['Male', 2]]).toarray() array([[0., 1., 0., 0.], [1., 0., 1., 0.]]) """ @_deprecate_positional_args def __init__(self, *, categories='auto', drop=None, sparse=True, dtype=np.float64, handle_unknown='error'): self.categories = categories self.sparse = sparse self.dtype = dtype self.handle_unknown = handle_unknown self.drop = drop def _validate_keywords(self): if self.handle_unknown not in ('error', 'ignore'): msg = ("handle_unknown should be either 'error' or 'ignore', " "got {0}.".format(self.handle_unknown)) raise ValueError(msg) # If we have both dropped columns and ignored unknown # values, there will be ambiguous cells. This creates difficulties # in interpreting the model. if self.drop is not None and self.handle_unknown != 'error': raise ValueError( "`handle_unknown` must be 'error' when the drop parameter is " "specified, as both would create categories that are all " "zero.") def _compute_drop_idx(self): if self.drop is None: return None elif isinstance(self.drop, str): if self.drop == 'first': return np.zeros(len(self.categories_), dtype=np.object) elif self.drop == 'if_binary': return np.array([0 if len(cats) == 2 else None for cats in self.categories_], dtype=np.object) else: msg = ( "Wrong input for parameter `drop`. Expected " "'first', 'if_binary', None or array of objects, got {}" ) raise ValueError(msg.format(type(self.drop))) else: try: self.drop = np.asarray(self.drop, dtype=object) droplen = len(self.drop) except (ValueError, TypeError): msg = ( "Wrong input for parameter `drop`. Expected " "'first', 'if_binary', None or array of objects, got {}" ) raise ValueError(msg.format(type(self.drop))) if droplen != len(self.categories_): msg = ("`drop` should have length equal to the number " "of features ({}), got {}") raise ValueError(msg.format(len(self.categories_), len(self.drop))) missing_drops = [(i, val) for i, val in enumerate(self.drop) if val not in self.categories_[i]] if any(missing_drops): msg = ("The following categories were supposed to be " "dropped, but were not found in the training " "data.\n{}".format( "\n".join( ["Category: {}, Feature: {}".format(c, v) for c, v in missing_drops]))) raise ValueError(msg) return np.array([np.where(cat_list == val)[0][0] for (val, cat_list) in zip(self.drop, self.categories_)], dtype=np.object) def fit(self, X, y=None): """ Fit OneHotEncoder to X. Parameters ---------- X : array-like, shape [n_samples, n_features] The data to determine the categories of each feature. y : None Ignored. This parameter exists only for compatibility with :class:`sklearn.pipeline.Pipeline`. Returns ------- self """ self._validate_keywords() self._fit(X, handle_unknown=self.handle_unknown) self.drop_idx_ = self._compute_drop_idx() return self def fit_transform(self, X, y=None): """ Fit OneHotEncoder to X, then transform X. Equivalent to fit(X).transform(X) but more convenient. Parameters ---------- X : array-like, shape [n_samples, n_features] The data to encode. y : None Ignored. This parameter exists only for compatibility with :class:`sklearn.pipeline.Pipeline`. Returns ------- X_out : sparse matrix if sparse=True else a 2-d array Transformed input. """ self._validate_keywords() return super().fit_transform(X, y) def transform(self, X): """ Transform X using one-hot encoding. Parameters ---------- X : array-like, shape [n_samples, n_features] The data to encode. Returns ------- X_out : sparse matrix if sparse=True else a 2-d array Transformed input. """ check_is_fitted(self) # validation of X happens in _check_X called by _transform X_int, X_mask = self._transform(X, handle_unknown=self.handle_unknown) n_samples, n_features = X_int.shape if self.drop_idx_ is not None: to_drop = self.drop_idx_.copy() # We remove all the dropped categories from mask, and decrement all # categories that occur after them to avoid an empty column. keep_cells = X_int != to_drop n_values = [] for i, cats in enumerate(self.categories_): n_cats = len(cats) # drop='if_binary' but feature isn't binary if to_drop[i] is None: # set to cardinality to not drop from X_int to_drop[i] = n_cats n_values.append(n_cats) else: # dropped n_values.append(n_cats - 1) to_drop = to_drop.reshape(1, -1) X_int[X_int > to_drop] -= 1 X_mask &= keep_cells else: n_values = [len(cats) for cats in self.categories_] mask = X_mask.ravel() feature_indices = np.cumsum([0] + n_values) indices = (X_int + feature_indices[:-1]).ravel()[mask] indptr = np.empty(n_samples + 1, dtype=np.int) indptr[0] = 0 np.sum(X_mask, axis=1, out=indptr[1:]) np.cumsum(indptr[1:], out=indptr[1:]) data = np.ones(indptr[-1]) out = sparse.csr_matrix((data, indices, indptr), shape=(n_samples, feature_indices[-1]), dtype=self.dtype) if not self.sparse: return out.toarray() else: return out def inverse_transform(self, X): """ Convert the data back to the original representation. In case unknown categories are encountered (all zeros in the one-hot encoding), ``None`` is used to represent this category. Parameters ---------- X : array-like or sparse matrix, shape [n_samples, n_encoded_features] The transformed data. Returns ------- X_tr : array-like, shape [n_samples, n_features] Inverse transformed array. """ check_is_fitted(self) X = check_array(X, accept_sparse='csr') n_samples, _ = X.shape n_features = len(self.categories_) if self.drop_idx_ is None: n_transformed_features = sum(len(cats) for cats in self.categories_) else: n_transformed_features = sum( len(cats) - 1 if to_drop is not None else len(cats) for cats, to_drop in zip(self.categories_, self.drop_idx_) ) # validate shape of passed X msg = ("Shape of the passed X data is not correct. Expected {0} " "columns, got {1}.") if X.shape[1] != n_transformed_features: raise ValueError(msg.format(n_transformed_features, X.shape[1])) # create resulting array of appropriate dtype dt = np.find_common_type([cat.dtype for cat in self.categories_], []) X_tr = np.empty((n_samples, n_features), dtype=dt) j = 0 found_unknown = {} for i in range(n_features): if self.drop_idx_ is None or self.drop_idx_[i] is None: cats = self.categories_[i] else: cats = np.delete(self.categories_[i], self.drop_idx_[i]) n_categories = len(cats) # Only happens if there was a column with a unique # category. In this case we just fill the column with this # unique category value. if n_categories == 0: X_tr[:, i] = self.categories_[i][self.drop_idx_[i]] j += n_categories continue sub = X[:, j:j + n_categories] # for sparse X argmax returns 2D matrix, ensure 1D array labels = np.asarray(sub.argmax(axis=1)).flatten() X_tr[:, i] = cats[labels] if self.handle_unknown == 'ignore': unknown = np.asarray(sub.sum(axis=1) == 0).flatten() # ignored unknown categories: we have a row of all zero if unknown.any(): found_unknown[i] = unknown # drop will either be None or handle_unknown will be error. If # self.drop_idx_ is not None, then we can safely assume that all of # the nulls in each column are the dropped value elif self.drop_idx_ is not None: dropped = np.asarray(sub.sum(axis=1) == 0).flatten() if dropped.any(): X_tr[dropped, i] = self.categories_[i][self.drop_idx_[i]] j += n_categories # if ignored are found: potentially need to upcast result to # insert None values if found_unknown: if X_tr.dtype != object: X_tr = X_tr.astype(object) for idx, mask in found_unknown.items(): X_tr[mask, idx] = None return X_tr def get_feature_names(self, input_features=None): """ Return feature names for output features. Parameters ---------- input_features : list of str of shape (n_features,) String names for input features if available. By default, "x0", "x1", ... "xn_features" is used. Returns ------- output_feature_names : ndarray of shape (n_output_features,) Array of feature names. """ check_is_fitted(self) cats = self.categories_ if input_features is None: input_features = ['x%d' % i for i in range(len(cats))] elif len(input_features) != len(self.categories_): raise ValueError( "input_features should have length equal to number of " "features ({}), got {}".format(len(self.categories_), len(input_features))) feature_names = [] for i in range(len(cats)): names = [ input_features[i] + '_' + str(t) for t in cats[i]] if self.drop_idx_ is not None and self.drop_idx_[i] is not None: names.pop(self.drop_idx_[i]) feature_names.extend(names) return np.array(feature_names, dtype=object) class OrdinalEncoder(_BaseEncoder): """ Encode categorical features as an integer array. The input to this transformer should be an array-like of integers or strings, denoting the values taken on by categorical (discrete) features. The features are converted to ordinal integers. This results in a single column of integers (0 to n_categories - 1) per feature. Read more in the :ref:`User Guide `. .. versionadded:: 0.20 Parameters ---------- categories : 'auto' or a list of array-like, default='auto' Categories (unique values) per feature: - 'auto' : Determine categories automatically from the training data. - list : ``categories[i]`` holds the categories expected in the ith column. The passed categories should not mix strings and numeric values, and should be sorted in case of numeric values. The used categories can be found in the ``categories_`` attribute. dtype : number type, default np.float64 Desired dtype of output. Attributes ---------- categories_ : list of arrays The categories of each feature determined during fitting (in order of the features in X and corresponding with the output of ``transform``). See Also -------- sklearn.preprocessing.OneHotEncoder : Performs a one-hot encoding of categorical features. sklearn.preprocessing.LabelEncoder : Encodes target labels with values between 0 and n_classes-1. Examples -------- Given a dataset with two features, we let the encoder find the unique values per feature and transform the data to an ordinal encoding. >>> from sklearn.preprocessing import OrdinalEncoder >>> enc = OrdinalEncoder() >>> X = [['Male', 1], ['Female', 3], ['Female', 2]] >>> enc.fit(X) OrdinalEncoder() >>> enc.categories_ [array(['Female', 'Male'], dtype=object), array([1, 2, 3], dtype=object)] >>> enc.transform([['Female', 3], ['Male', 1]]) array([[0., 2.], [1., 0.]]) >>> enc.inverse_transform([[1, 0], [0, 1]]) array([['Male', 1], ['Female', 2]], dtype=object) """ @_deprecate_positional_args def __init__(self, *, categories='auto', dtype=np.float64): self.categories = categories self.dtype = dtype def fit(self, X, y=None): """ Fit the OrdinalEncoder to X. Parameters ---------- X : array-like, shape [n_samples, n_features] The data to determine the categories of each feature. y : None Ignored. This parameter exists only for compatibility with :class:`sklearn.pipeline.Pipeline`. Returns ------- self """ self._fit(X) return self def transform(self, X): """ Transform X to ordinal codes. Parameters ---------- X : array-like, shape [n_samples, n_features] The data to encode. Returns ------- X_out : sparse matrix or a 2-d array Transformed input. """ X_int, _ = self._transform(X) return X_int.astype(self.dtype, copy=False) def inverse_transform(self, X): """ Convert the data back to the original representation. Parameters ---------- X : array-like or sparse matrix, shape [n_samples, n_encoded_features] The transformed data. Returns ------- X_tr : array-like, shape [n_samples, n_features] Inverse transformed array. """ check_is_fitted(self) X = check_array(X, accept_sparse='csr') n_samples, _ = X.shape n_features = len(self.categories_) # validate shape of passed X msg = ("Shape of the passed X data is not correct. Expected {0} " "columns, got {1}.") if X.shape[1] != n_features: raise ValueError(msg.format(n_features, X.shape[1])) # create resulting array of appropriate dtype dt = np.find_common_type([cat.dtype for cat in self.categories_], []) X_tr = np.empty((n_samples, n_features), dtype=dt) for i in range(n_features): labels = X[:, i].astype('int64', copy=False) X_tr[:, i] = self.categories_[i][labels] return X_tr