type t =
[ `BaseEstimator | `DictVectorizer | `Object | `TransformerMixin ] Obj.tval of_pyobject : Py.Object.t -> tval to_pyobject : [> tag ] Obj.t -> Py.Object.tval create :
?dtype:Py.Object.t ->
?separator:string ->
?sparse:bool ->
?sort:bool ->
unit ->
tTransforms lists of feature-value mappings to vectors.
This transformer turns lists of mappings (dict-like objects) of feature names to feature values into Numpy arrays or scipy.sparse matrices for use with scikit-learn estimators.
When feature values are strings, this transformer will do a binary one-hot (aka one-of-K) coding: one boolean-valued feature is constructed for each of the possible string values that the feature can take on. For instance, a feature 'f' that can take on the values 'ham' and 'spam' will become two features in the output, one signifying 'f=ham', the other 'f=spam'.
However, note that this transformer will only do a binary one-hot encoding when feature values are of type string. If categorical features are represented as numeric values such as int, the DictVectorizer can be followed by :class:`sklearn.preprocessing.OneHotEncoder` to complete binary one-hot encoding.
Features that do not occur in a sample (mapping) will have a zero value in the resulting array/matrix.
Read more in the :ref:`User Guide <dict_feature_extraction>`.
Parameters ---------- dtype : callable, optional The type of feature values. Passed to Numpy array/scipy.sparse matrix constructors as the dtype argument. separator : string, optional Separator string used when constructing new features for one-hot coding. sparse : boolean, optional. Whether transform should produce scipy.sparse matrices. True by default. sort : boolean, optional. Whether ``feature_names_`` and ``vocabulary_`` should be sorted when fitting. True by default.
Attributes ---------- vocabulary_ : dict A dictionary mapping feature names to feature indices.
feature_names_ : list A list of length n_features containing the feature names (e.g., 'f=ham' and 'f=spam').
Examples -------- >>> from sklearn.feature_extraction import DictVectorizer >>> v = DictVectorizer(sparse=False) >>> D = {'foo': 1, 'bar': 2}, {'foo': 3, 'baz': 1} >>> X = v.fit_transform(D) >>> X array([2., 0., 1.],
[0., 1., 3.]) >>> v.inverse_transform(X) == {'bar': 2.0, 'foo': 1.0}, {'baz': 1.0, 'foo': 3.0} True >>> v.transform('foo': 4, 'unseen_feature': 3) array([0., 0., 4.])
See also -------- FeatureHasher : performs vectorization using only a hash function. sklearn.preprocessing.OrdinalEncoder : handles nominal/categorical features encoded as columns of arbitrary data types.
val fit : ?y:Py.Object.t -> x:Py.Object.t -> [> tag ] Obj.t -> tLearn a list of feature name -> indices mappings.
Parameters ---------- X : Mapping or iterable over Mappings Dict(s) or Mapping(s) from feature names (arbitrary Python objects) to feature values (strings or convertible to dtype). y : (ignored)
Returns ------- self
val fit_transform :
?y:Py.Object.t ->
x:[> `ArrayLike ] Np.Obj.t ->
[> tag ] Obj.t ->
[> `ArrayLike ] Np.Obj.tLearn a list of feature name -> indices mappings and transform X.
Like fit(X) followed by transform(X), but does not require materializing X in memory.
Parameters ---------- X : Mapping or iterable over Mappings Dict(s) or Mapping(s) from feature names (arbitrary Python objects) to feature values (strings or convertible to dtype). y : (ignored)
Returns ------- Xa : array, sparse matrix Feature vectors; always 2-d.
val get_feature_names : [> tag ] Obj.t -> Py.Object.tReturns a list of feature names, ordered by their indices.
If one-of-K coding is applied to categorical features, this will include the constructed feature names but not the original ones.
Get parameters for this estimator.
Parameters ---------- deep : bool, default=True If True, will return the parameters for this estimator and contained subobjects that are estimators.
Returns ------- params : mapping of string to any Parameter names mapped to their values.
val inverse_transform :
?dict_type:Py.Object.t ->
x:[> `ArrayLike ] Np.Obj.t ->
[> tag ] Obj.t ->
Py.Object.tTransform array or sparse matrix X back to feature mappings.
X must have been produced by this DictVectorizer's transform or fit_transform method; it may only have passed through transformers that preserve the number of features and their order.
In the case of one-hot/one-of-K coding, the constructed feature names and values are returned rather than the original ones.
Parameters ---------- X : array-like, sparse matrix of shape (n_samples, n_features) Sample matrix. dict_type : callable, optional Constructor for feature mappings. Must conform to the collections.Mapping API.
Returns ------- D : list of dict_type objects, length = n_samples Feature mappings for the samples in X.
val restrict :
?indices:bool ->
support:[> `ArrayLike ] Np.Obj.t ->
[> tag ] Obj.t ->
Py.Object.tRestrict the features to those in support using feature selection.
This function modifies the estimator in-place.
Parameters ---------- support : array-like Boolean mask or list of indices (as returned by the get_support member of feature selectors). indices : boolean, optional Whether support is a list of indices.
Returns ------- self
Examples -------- >>> from sklearn.feature_extraction import DictVectorizer >>> from sklearn.feature_selection import SelectKBest, chi2 >>> v = DictVectorizer() >>> D = {'foo': 1, 'bar': 2}, {'foo': 3, 'baz': 1} >>> X = v.fit_transform(D) >>> support = SelectKBest(chi2, k=2).fit(X, 0, 1) >>> v.get_feature_names() 'bar', 'baz', 'foo' >>> v.restrict(support.get_support()) DictVectorizer() >>> v.get_feature_names() 'bar', 'foo'
val set_params : ?params:(string * Py.Object.t) list -> [> tag ] Obj.t -> tSet the parameters of this estimator.
The method works on simple estimators as well as on nested objects (such as pipelines). The latter have parameters of the form ``<component>__<parameter>`` so that it's possible to update each component of a nested object.
Parameters ---------- **params : dict Estimator parameters.
Returns ------- self : object Estimator instance.
Transform feature->value dicts to array or sparse matrix.
Named features not encountered during fit or fit_transform will be silently ignored.
Parameters ---------- X : Mapping or iterable over Mappings, length = n_samples Dict(s) or Mapping(s) from feature names (arbitrary Python objects) to feature values (strings or convertible to dtype).
Returns ------- Xa : array, sparse matrix Feature vectors; always 2-d.
Attribute feature_names_: get value or raise Not_found if None.
Attribute feature_names_: get value as an option.
val to_string : t -> stringPrint the object to a human-readable representation.
val show : t -> stringPrint the object to a human-readable representation.
val pp : Format.formatter -> t -> unitPretty-print the object to a formatter.